Answer:
Son's present age: 10
Father's present age: 35
Explanation:
Let f = father's age
Let s = son's age
1) Set up a system of equations.
4s - 5 = f
f + s = 45
2) Solve using substitution or elimination.
4s - 5 + s = 45
5s - 5 = 45
5s = 45 + 5
5s = 50
s = 50/5
s = 10
3) Substitute 10 into s.
f + 10 = 45
f = 45 - 10
f = 35