The Given word is WEBPAGE. After making required changes , we get the given word in the following form :

VFAOBFF.

Hence, the letter F will appear thrice.

MERCIFUL   =>   CEFILMRU   => BDEHKLQT

Given word : CONTEXTUAL

After making changes as per given in the question , the above word becomes as follows:

XTUALCONTE . Hence, 4th letter from the right end is O.

quicker method:

    Total no of letters in the given word = 10.

    4th letter from the right means (10 - 4 + 1 =) 7th letter from the left of the word obtained after rearrangement. Again, read the question , we come to know that, the positions of the second and seventh letters are interchanged. Hence the required letter is the second letter of the given word which is O.

6th to the left of 17th letter to the right of 7th letter from the left = 6th to the left of (17+7 =) 24th letter from the left = (24-6 =) 18th letter from the left.

Thus, we have to count from the left and we have to find out 18th letter from the left that falls into the second section of English alphabet.

Here, both the first half and the second half of the English alphabet have been reversed and we have to count from the left end, then the required letter can be found out using the formula given below. Suppose , the first and the second reversed sections of the English alphabet are α and  βrespectively.Then,

  The required letter = 2α+β+1-(required position of letter from left side)

Therefore, The required letter = 26 + 13 + 1 - 18 = 22 = V

2nd letter to the left of 17th letter from the right means (2 + 17 = ) 19th letter from the right = (26 - 19 + 1 =) 8th letter from the left end , i.e H.  Thus, 8th letter falls into the second section of the reversed sequence. Now, the sequence FGHIJ is reversed and becomes JIHGF. Clearly, position of H remains unchanged. Hence the required letter is H.

If the first half of the English alphabet is reversed and the remaining part has been left undisturbed, then it becomes very easy to find out the required letters, if required letters come in the first half. According to the question, 10th to the left of 16th letter from the left = (16 - 10 =) 6th letter from the left in new series.

=>  6th letter from the left in new series = (13 + 1 - 6=) 8th letter from the left in the original series, i.e H.

First letters are common. Second letters are:b, c, c, c, c. One of the four words having c is the last word. Let us see the third letters now ,there are: t, c, q, h. Clearly t is the last. Hence Actuate is the last word. 

The given word is VITREOUS. Of which , TRSV are the consonants and IEOU are the vowels. Now, after making the changes as given in the question  we get following arrangment: RSTVEIOU.

Again from precalculation, we know that second to the right of fourth  from the left means (2+4=) 6th from the left. i.e I