Can someone me on this one question?

A+30 = 60
a = 30

a + 2b = 60
30+2b = 60
2b = 30
b = 15

5b - 5c = 60
5(15) - 5c = 60
5c = 15
c = 3

10c + d = 60
10(3) + d = 60
30 + d = 60
d = 30

2d + 6e = 180 - 60
2(30) + 6e = 120
6e = 60
e = 10

4f + 4e = 120
4f + 4(10) = 120
4f = 80
f = 20