First you must remember the Distributive property. This states the following:
Notice that the terms inside the parentheses ("a" and "b") are multiplied by "c", which is outside of the parentheses.
Therefore, having the following expression:
You can simplify it by applying the Distributive property. So, you have to multiply the terms inside the parentheses by the number 6 that is outside.
Then, the expression simplified is: