One third the difference of two number is 12. if the larger number is 9, what is the sum of the two numbers

The sum of the two numbers is -18.

Step-by-step explanation:

You can work your way through the problem starting with ...

1/3 the difference of two numbers is 12

Since 3 times 12 is 36, the difference of the two numbers is 36.

Then you are told ...

the larger number is 9

so the smaller number will be 9 less the difference, or ...

smaller number = 9 - 36 = -27.

Now, you know both numbers, so you know there sum is ..

9 + (-27) = -18 . . . . . sum of the two numbers

You can work it also using L for the larger number, D for the difference. Then the smaller number is (L-D) and the sum is ...

sum = L + (L -D) = 2L - D

Filling in the values given for the larger number and the difference, you have ...

sum = 2·9 - 3·12 = 18 -36 = -18 . . . . . as before