the length of a rectangle is 10 feet longer than the width. If the perimeter is 86 feet, find the length and width

L = 10+W

P = 2L + 2W   and   P = 86  --->  2L + 2W = 86 

Substituting:  2(10+W) + 2W = 86

                      20 + 2W + 2W = 86

                             20 + 4W = 86

                                     4W = 66

                                       W = 16.5              L = 16.5 + 10  =  26.5