You can put this solution on YOUR website! The formula for the area of a parallelogram is the same as for the area of a rectangle: base times height. So
You could go ahead and perform the multiplication on the left and solve the resulting quadratic equation either by factoring or with the quadratic formula. But it is much easier to solve the problem by trial and error: find two numbers whose product is 91 that can be expressed in the form (x+1) and (2x+1).