A 90.0-g disk traveling 3.00 m/s to the right collides with a 75.0-g disk traveling

Question

8.00 m/s to the left. After the collision, the heavier disk is traveling 7.00 m/s to the
left. What is the velocity of the lighter disk after the collision?

Do I have this setup right?
(90.0*3.00+75.0*(-)8.00-75.0*(-)7.00) ÷90.0

Answer 1

coolio, momentum problem

m₁v₁ + m₂v₂ = m₁v₁' + m₂v₂'

(90.0 g)(3.00 m/s) + (75.0 g)(-8.00 m/s) = (90.0 g)(-7.00 m/s) + (75.0 g)v₂'

If you solve it out, v₂' should be 4 m/s

Answer 2

Made a mistake, I had to divide by 75.0 so that the 90.0 cancels out. Thank you