let

x = the age of the father

y = the age of the son

father is 27 years older than his son

x = y + 27

the sum of their ages is 55 years

x + y = 55

by solving the system of equations

x = y + 27

x + y = 55

we find

x = 41 years

y = 14 years

The son is 14 years old.