Here's a hint and one way of solving the problem (there are other methods too):
Since you have two equations that define what Y is, set them equal to each other and solve for X. i.e. -4X+5 = -3X+4. They should be equal to each other, as they both are equal to Y.
Once you get the value for X, you can plug that X value back into one of the equations (it doesn't matter which one) to solve for Y.
Good luck!