Coding and Decoding Questions

If 'x' means '-', '-' means 'x', '+' means '/' and '/' means '+', then what is the value of 15 - 2 / 900 + 90 x 100?

 In a certain code language, “PRANK” is written as “RUESQ”. How is “RATES” written in that code language?

In a certain code language, '+' represents 'x', '-' represents '+', 'x' represents '÷' and '÷' represents '-'. What is the answer to the following question?

80 + 2 ÷ 25 + 5 - 10 = ?

If "*" denotes "added to", "&" denotes "divided by", "@" denotes "multiplied by" and "%" denotes "subtracted from", then 136 & 8 @ 7 % 3 * 7 = ?

If 80&10 = -8, 50&2 = -25 and 80&16 = -5, then find the value of 20&5 = ?

In a certain code language, “MOCKS” is written as “NNDJT”. How is “FLAME” written in that code language?

If EXPLAIN is coded as BUMIXFK, then how will GYM be coded as?

If P denotes multiply, T denotes subtraction, M denotes addition, B denotes division then 28B7P8T6M4 = ?