What is the correct first step to solving the following system using substitution?
4x 5y=7
y=3x-10

4(3x - 10) + 5y = 7
4x + 3y = 7(3x - 10)
4(3x) + 5(-10) = 7
(3x - 10)(4x + 3y) = 7
4x + 5(3x - 10) =