I'll set you up, and then I'll leave it for you to finish.
Let and represent the width and length of the triangle respectively. We know that the length of rectangle is one more unit than its width:
-- (1)
and we're told the area of the rectangle is 30 sq units:
-- (2)
Now substitute (1) into (2) to get
Can you continue and solve the quadratic equation?
(you'll see that one of the solutions to the quadratic equation won't work)