Equation in slope intercept form for a line that passes through (1,5) and (1,1)

Find the solution of system of equation y= x-4 y=4x+2

Any is very appreciated! (picture is provided below)not sure how to do this at all won't lie

At the beginning of 1974/75,2 years a man invested #2000 in a bank at 12.5% compound interest, if it degree #650 at the end of each two years to pay his son's school fees, after payment of interest to pay his son's school fees, how much did he have left at the beginning of the 1978/79 school year?