Question 350070
Let x represent c's age. So the ages of the other people in terms of c, are:
b = 3x
a = 3x + 4

We know that; a + b + c = 25
Substitute in terms of x.

3x + 4 + 3x + x = 25
7x + 4 = 25
7x = 21
x = 3

We know that b = 3x
So, b = 3(3) = 9