If the average of a,a+3,a+6,a+9 and a+12 is 10 ,then a is equal to-

A 1

B 2

C 3

D 4

Correct Answer: Option D

এখানে , (a+a+3+a+6+a+9+a+12)/5=10
          বা, 5a+30=50
          বা,5a=20
          বা,a=4