30-f+8f=30
30+7f=30
Move +30 to the right side. Sign changes from +30 to -30.
30-30+7f=30-30
7f=0
Divde by 7
7f/7=0/7
Cross out 7 and 7, divide by 7. Becomes 1*1*f=f
f=0
Answer: f=0
X is 35, if you follow the rules of alternate angles
22 + (30 - 4) divided by 2
30 - 4 = 26
26/2 = 13
22 + 13 = 35
35
18 + (22 - 4) divided by 6
22 - 4 = 18
18 divided by 6 = 3
18 + 3 = 21
21
