Answer:
Step-by-step explanation:
Given
7.2, a, b, 3 are in A.P


as
a, b, 3 are also in A.P

Putting 










Now, plugging
in 




Therefore,
1. 2(10)
4(20)
6(30)
I only know the answer to number 1 sorry. :/
Step-by-step explanation:
None of these,
a(under root),a, a(square)
this is the correct answer