How would I put the following equations into y=mx+b form?

x+y=4

-4x+y=9

The first one you would move x to the other side making it negative, or subtract x from both sides giving:

y=-x+4
-1 is the m and 4 is the b

For the second one, you do the same thing. Add 4x to each side canceling the 4x on the left, or move 4x to the other side making it positive.
y=4x+9
4 is the m and 9 is the b