Question 1145590
3f=a+4
a=3f-4

a+3+f+3=30

3f-4+3+f+3=30
combine terms
4f+2=30
4f=28
f=7
a=21-4
a=17
check
7+3+17+3=30
10+20=30
ok
3F=a+4
21=21
ok