Question 1082213
a)

We need to solve the system:

1) C = 13
2)C*a^4 = 31,213

So C = 13 and a^4 = 2,401
             a = 7

b)

We need to solve the system:

1) C*a = 16
2)C*a^3 = 9

So a^2 = 9/16
     a = 3/4 and C = 64/3

@natolino_