00:01
I use a graph to show how to solve this question.
00:06
We know that the rectangular swimming pool is 30 feet by 40 feet, that is the area of the blue region.
00:21
We know that there is a rectangular strip of grass of uniform whites that is around the swimming pool, and the area of this strip is 624 square feet.
00:42
That is the area of the green region.
00:49
And the big rectangular, its white is 30 plus 2x, and its length is 40 plus 2x.
01:07
And the area of the grass is just the difference of the bigger rectangle.
01:16
And the smaller rectangle.
01:19
And hence, the area of the bigger rectangle is 30 plus 2x times 40 plus 2x and the area of the small rectangle, which is the area of the swimming pool, is 30 times 40.
01:41
And their difference is the area of the grass, which is 624.
01:47
We can simplify this equation as 4x squared plus 140x equals 6244...