Your task is to find the smallest possible value of x. You have the following equations:
x + a + b = 0.55 .... (1)
x + c = 0.6 .... (2)
c + d + e = 0.45 .... (3)
b + e = 0.16 .... (4)
a + d = 0.24 .... (5)
and you want the smallest value of x for which these equations will be consistent.
So I get x = 0.15 which is equivalent to 15% so yes you're correct.
(No doubt someone will give a simple two line confirmation of this).