Step-by-step explanation:
y = 7x - 3
To make x the subject, you need to isolate it. (Get x by itself)
y = 7x - 3
Add 3 on both sides...
y + 3 = 7x
Divide by 7 (Maybe your teacher wants 7x = y = 3 but if she doesn't and wants x completely by itself here's the answer)
x = y/7 + 3/6