Substitution can also involve more complicated problems, like 5x^2 + 2y -6 = y, where y = -1 and x = 4. Just substitute in the same way, placing the value of each variable in place of the letter and simplifying.
what dose this ^ mean is it like this
5 * 42 + 2 * -1 - 6
The ^ symbol is used to indicate that the following number is an exponent.
5x^2 means 5*(x squared) or 5*x*x.
If your formula is really
5x^2 + 2y -6 = y, that would be the same thing as writing
5x^2 -6 = -y
or
y = 6 - 5x^2
When x = 4, clearly y is NOT -1.
So I don't quite understand what the problem is asking