Let the length of the pool = l
and width = w
length of a rectangular swimming pool is 10 feet longer than its width.
So , l=w+10
Perimeter of the rectangle = 100 feet
It means
2(l+w) = 100
So we have two equations
l=w+10 and 2(l+w) = 100 or l+w = 50
Plug l = w+10 into l+w =50
So we get
w+10+w= 50
Subtract 10 from both sides
2w= 40
divide both sides by 2
w=20
And l = w+10 = 20+10 = 30
So l= 30 and w= 20
So dimensions are
length of the rectangle = 30 feet
width of the rectangle = 20 feet
So Option B is correct.