How do u work 4y+3=3y+x using substitution

Hello from MrBillDoesMath!

I think more info is needed but here's a first step.

Suppose

4y + 3 = 3y + x

Subtracting 3y from each side gives

4y - 3y + 3 = (3y - 3y) + x or

y + 3 = x.

Subtracting 3 from both sides gives:

y = x - 3.

So ... if you have another equation involving x and y you could substitute the above y value (i. e. x-3) for every occurrence of y

Regards, MrB