a + b = 8

a + c = 5

Subtracting the second equation from the first:

b - c = 3

b + c = 3

Adding the two equations together:

2b = 6

b = 3

Since a + b = 8 and b = 3: a + 3 = 8 ---> a = 5

Since a + c = 5 and a = 5: c = 0

From these values, you can get the answer.