In order to solve this question we first have to break down the terms.
Sum = Adding
Times = Multiplying.
The question states "3 times the sum of a number n and 12 is 45". In written form, it would be the following:
3(12+n) = 45
To solve this you first divide both sides by three and you'd be left with the following:
(12+n) = 15.
Then subtract 12 from both sides. Leaving you with:
n = 3
