Hi,
If you use y from the second equation in the first you have 4x+2(5-5x)=7, this reduces to 4x+10-10x=7, collecting like terms gives -6x=-3 or x=1/2 putting this value in the second equation gives y=5-5/2=10/2-5/2=5/2 so the solution is x=1/2, y=5/2. This is the point where the two lines intercect and can be seen if you graph both lines on the same graph.
Jim