The length of a rectangle is four more than triple the width. If the perimeter is 96 inches, find the dimensions.

Answer 1

You know l = 3w +4 and that P = 96 = 2l + 2w.

Rearrange one of the equations to find one variable in terms of the other, then plug into the second equation and solve.

Alternatively, since the equations are linear, you can write them in the same form and subtract double the 1st equation from the second in order to eliminate l and get an equation in terms of w.

This is a 2nd year algebra problem, not a differential equation problem.