Direction: what should come in place at question mark(?).

$$ {1\over 8}×(223+?)=71$$

The number, whose square is equal to the difference between the squares of 975 and 585, is: 

[(169×121)÷(11×13)]-3=?

$$ {\sqrt{784}} × \sqrt{6.25} + 56\%\ of\ 450=?+186$$

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

If 2x + 3y - 5z = 18 , 3x + 2y + z = 29 and x + y + 3z = 17 , then what is the value of xy + yz + zx ? 

What is the value of x $$ {0.081\over x}={0.09\over10}$$ ?

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