Question

On the problem 9x+7y=4

x=23-4y
solve by substitution

Do you mean to put 9 in the place of x=23-4y (9x=23-4y)

Answer 1

It would look like this...9(23-4y)+7y=4

Then you simplify
9*23=207
9*-4y=-36y
so you now have
207-36y+4y
Combine like terms
-36y+4y=-32
-32y=4
Finally you divide
the end result is y=-8