To find what should be added to 3 times 39 to get 12 times 39, we can set up an equation.
Let's represent the unknown value to be added as "x".
3 times 39 + x = 12 times 39
Now, let's solve for "x":
3 * 39 + x = 12 * 39
117 + x = 468
Subtract 117 from both sides to isolate "x":
x = 468 - 117
x = 351
So, 351 should be added to 3 times 39 to get 12 times 39.