Since width is the smaller value, set width=x. That wold mean that length=x+3. Since Area=width*length, 40=x(3+x). Distribute the x to give you 40=3x+x^2. Set the equation equal to 0 giving you x^2+3x-40=0. Factor the equation to give you (x+8)(x-5)=0. Set each factor equal to 0. x+8=0 gives you x=-8 & x=-5 gives you x=5. Since we're working with lengths of objects, it can't be negative. Therefore, your width is 5. To find length, substitute width into the original expression (x+3). Therefore, length is 5+3=8.
