What is (–5) 2 and how do i solve

Problem melissa is her dad build a walkway in their backyard. the walkway will be 54 feet long and 1.5 feet wide. the local hardware store sells tiles which are 1.5 by 1.5 feet and come in boxes of 12. how many boxes of tiles do they need?

How do you use the elimination method for this question? explain, because i really want to understand!

Need 50 will mark brainliest answer. find the lengths of all the sides and the measures of the angles.