If (a + b) / b = 5 ---> a/b + b/b = 5 ---> a/b + 1 = 5 ---> a/b = 4
If (b + c) / c = 4 ---> b/c + c/c = 4 ---> b/c + 1 = 4 ---> b/c = 3 ---> c/b = 1/3
a/b + c/b = 4 + 1/3 = 13/3 and a/b + c/b = (a + c)/b ---> (a + c)/b = 13/3
Since b/c = 3 ---> b = 3c
(a + c)/b = 13/3 and b = 3c ---> (a + c)/(3c) = 13/3 ---> (a + c)/c = 13