PLZ HELP THIS IS DUE TOMMOROW AND I AM STUCK if the perimeter of a rectangle is 78 cm, and its length equals 3+2(width) what is an equation to find the width and length

since perimeter is the total of the length plus length plus width plus width:
L+L+W+W= 78 cm (given in the problem) as the total perimeter; and remember the length (we are told in the problem) is equal to 2 times width. so:
3 +2w+3+2w=78
6 +4w=78
6+4w-6=78-6
4w=72
w=18