Questions

A - A - A = 20
B - B - B = 15
C - C - C = 25

A = -20
B = -15
C = -25

=> A + B + C = (-20)+(-15)+(-25) = -20 - 15 - 25 = -60.

Galileo Galilei (1564-1642) was an Italian Astronomer who

1) Discovered 4 satellites of Jupiter

2) Developed Telescope

3) Discovered that the movement of pendulum produces a regular time measurement

He is Physicist, Mathematician, inventor, and philosopher Too.

Primary key helps us to identify a row uniquely in a relation

Sum of all numbers in each row and columns must be 15.

In last row to gt sum as 15 missing number must replaced by 1. 

The given math puzzle follows a logic that,

1 + 4 = 5 => 1 x 4 + 1 = 5

2 + 5 = 12 => 2 x 5 + 2 = 12

3 + 6 = 21 => 3 x 6 + 3 = 21

Similarly,

8 + 11 = > 8 x 11 + 8 = 96.

A Skeleton is what is whole but incomplete, have no eyes, yet can see. We can see, and see right through it. The largest part is one fourth of what it once was i.e body.