If 3x + 7y=75, 5x- 5y= 25, then the value of (x +y)=?

The smallest positive integer n for which 864 x n is a perfect cube, is: 

Find the value of x:
2³ × 3⁴ × 1080 ÷ 15 = 6^x

Find the value of given expression.

3 – (– 6) {– 2 – 9 – 3} ÷ 7{1 + (– 2) (– 1)}

The value of   $$ {(0.03)^2 - (0.01)^2}\over 0.03-0.01 $$

(0.04)^-1.5 on simplification gives: 

There are some boys and girls in a room. The square of the number of the girls is less than the square of the number of boys by 28. If there were two more girls, the number of boys would have been the same as that of the girls. The total number of the boys and girls in the room are

The simplified value of
$${{1\over 3}÷{1\over 3}×{1\over 3}\over{1\over 3}÷{1\over 3}of{1\over 3}}-{1\over 9}$$