If x=3 and y=3-4x, what is y?

Question

I'm trying to remember algrebra to help my 4th grade son.

Answer 1

When you have equations like this and you're given one of the variables, all you do is plug that variable value into the equation. 

Here we have x=3. That means that in our equation y=3-4x, the x can be replaced with the 3 as follows:

y=3-4(3). Multiply the 4 and 3.

y=3-12. Subtract 12 form 3.

y=-9. Answer.