Let x be how old the son is. We know that the dad is 3 times older and their sum is 48. Creating an equation to represent this situation gives us:
Divide both sides by 4
The son is 12 years old, but we want to find the age of the dad. Since we know the dad is 3 times older, multiply 12 with 3
The dad is 36 years old. Let me know if you need any clarifications, thanks!