What is the solution to this system of linear equations?

x + y = 4

x − y = 6

This is a simultaneous equation so you have to find the value of x or y. We can do this by adding the 2 equations. This would make 2x, and y + -y = nothing. 4 + 6 = 10. So we have the equation 2x = 10. Divide both sides by 2 and you get the value of x, which is 5. You then plug this into the orignal equation, either one will work. You get a value of -1 for y.
x = 5 when y = -1.