Question 316403
hey,

So for this one, we need to write down what we know:

n + 12 = n(2) 
n + 2*n(2) = 39 

We substitute n(2) into the second equation:

n + 2*(n + 12) = 39

n + 2n + 24 = 39

3n + 24 = 39

3n = 15 

n = 5

5 + 12 = n(2)

Therefore:

The big number is 17


I hope this helps!