64 is the product of two numbers, 4 and d, meaning that 4d = 64.
If you would like to find Donnie's score:
You can divide both sides of the equation by 4, so that the left side is now equal to (4 * d)/4, which is equal to d. The right side would be 64/4, which is equal to 16.
Now, you have the equation d = 16, meaning that Donnie's score is equal to 16.