Sally is 4 years older than Mark. Twice Sally's age plus 5 times Mark's age is equal to 64.

Sally is 4 years older than Mark. Twice Sally's age plus 5 times Mark's age is equal to 64.

Let Sally's age be s. Let Mark's age be m. We're given two equations:

1. s = m + 4
2. 2s + 5m = 64 <-- Since Twice means we multiply by 2

Substitute equation (1) into equation (2):
2(m + 4) + 5m = 64

Multiply through:
2m + 8 + 5m = 64

Group like terms:
(2 + 5)m + 8 = 64
7m + 8 = 64

Type this equation into the search engine and we get:
m = 8