Complete the series choosing the missing number: 

12, 15, 21, 24, 30 ______

Find the missing number.
10, 100, 200, 310, ?

Find the missing number?
15, 31, 64, 131, ?

In the following question, select the number which can be placed at the sign of question mark ( ?) from the given alternatives .

Find the value  (?) in the given figure.

In the following question, select the number which can be placed at the sign of question mark (?) from the given alternatives. 

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

$$ \sqrt{576}+\sqrt{841} =(?) $$