3times the sum of a number n and 12 is 45

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