let's say the two numbers are "a" and "b"
"a" being the smaller one, and "b" the larger one
so, their sum is 118, or a + b = 118
if 4 times the smallest, or 4*a or 4a
is subtracted from the largest, "b", so b - 4a
equals 18, so b - 4a = 18
thus

solve for "a", to find the smaller one
what's b? well, b = 118 - a