Based on the sentence, the adverbial clause is "after he finishes football practice". Adverbial clause is a set of words that is usually preceded by subordinating conjunctions such as after, if, etc.It usually answers the question when, where, what, how or by how much.
She can fit 3 squares along the 10 inch side and 6 squares along the 18 inch side. When you multiply 3 by 6 you get 18. The answer is not 20 because you cannot fit 20 3x3 squares.
