Four times a number, x, plus five times a number, y, equals 79. Ten times x minus 5 times y equals 5. Find the numbers by setting up a system of linear equations and solving the system using the elimination method.
a) x = 7, y = 9
b) x = 6, y = 11
c) x = 8, y = 10
d) x = -10, y = 7