I'm more visual, but if you're not, and this confuses you, ask me, and I'll explain it.
The answer is fully given in the picture below. Hope it helps!
3n-5=-48-40n
Move -40n to the other side. Sign changes from -40n to +40n.
3n+40n-5=-48= -48-40n+40n
3n+40n-5=-48
Move -5 to the other side.
3n+40n-5+5=-48+5
3n+40n=-43
43n=-43
Divide by 43 for both sides
43n/43=-43/43
n=-1
Answer: n=-1