Question 79987
say we call small number x
then the large number would be x+12
""The sum of the smaller number and twice the larger number is 39"" which translates into 
x+2(x+12)=39
x+2x+24=39
3x+24=39
3x=15
x=5

but x was the smaller number so to find the larger number we just have to add 12

5+12=17

17 is the larger number