Marcello is replacing a rectangular sliding glass door with dimensions of (x + 7) and (x + 3) feet. The area of the glass door is 45 square feet. What are the length and width of the door? Complete the explanation of how you got your answer.

I found the area of the glass door by multiplying the length by the width, which is _____. I set this product, which represents the area in terms of x equal to ____ . Then, I rewrote the equation so one side was 0 and solved for x and got x=____. A dimension of the door can't be negative so x = ____ .