What approximate value should come in the place of question mark (?) in the following question?
 (8423 + 3120 + 6543) ÷ (1536 + 377 + 189) = ?

If (x +y) = 6 and x² + y² = 20 then find the value of (x - y) ².

12 × 15 + 27 – ? = 28% of 400

How many perfect squares lie between 120 and 300? 

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

[(169×121)÷(11×13)]-3=?

Simplify the following equation.
$${(785.785.785+435.435.435) \over(785)^{2}+(435)^{2}-(785)(435)}$$

7 × 7 of 3 ÷ 3 -14 × P=7, then find out the value of P?