A garden designer designed a square decorative pool. The pool is surrounded by a walkway. On two opposite sides of the pool, the walkway is 8 feet. On the other two opposite sides, the walkway is 10 feet. The final design of the pool and walkway covers a total area of 1,440 square feet. The side length of the square pool is x.

Here's why:

The 4 and 8 on the left side combine to 12. The 5x and -3x on the right hand side combine to 2x.

This means the equation for choice D becomes 2x+12 = 2x-12

From here, subtract 2x from both sides. Doing so will cancel each copy of 2x and the x terms go away entirely. We're left with 12 = -12 which is a false statement since we don't have the same number on both sides. We have a contradiction instead, so there are no solutions here.

No matter what we replace x with in equation D, it will always be false.

If you graphed y = 2x+12 and y = 2x-12, you would find that the lines are parallel. Parallel lines never intersect. Intersection points are solution points, so this is a visual way to see that we don't have any solutions.