Find the exact value of the following question:

$$ 8\sqrt{?}÷14×3+9=21$$

Find the sum of 30²+31²+32²+________+80²

5-[4-{3-(3-3-6)}] is equal to:

A sum of Rs. 12,000, deposited at compound interest becomes double after 5 years. How much will it be after 20 years? 

Given that DE || BC, AD : DB = 3 : 4, find out ar(∆ADE)/ar(∆ABC)?

A sells a good to B at a profit of 20% and B sells it to C at a profit of 25%. If  C pays Rs. 225 for it, what was the cost price of A?

Simplify the following

  $${\sqrt { 10+{\sqrt { 25+ {\sqrt { 108 +\sqrt { 154+ \sqrt { 225} \ } \ } \ }} \ } } \ }\over \sqrt { 16+ 19.25×4^2} $$

Direction : What value should come in the place of question mark (?) in the following questions?

23 × 45 ÷ 15=?