Hello there, this problem is just basic addition, here is what it would look like

Solve it and we get 78.21
Answer:
Step-by-step explanation:
The answer is 26
"The number 39 is equal to"
39=
"thirteen subtracted from an unknown number"
r-13
Putting it together you have:
39=r-13
Why did you post it if it’s not a question lol
If he swan the length and the width of the pool it would be 21 x28 = 588 sq ft.
by swimming the length and the diagonal of the pool (25 ft) found that by using the pythagorean therom so now you are multiplying 21 x 25 = 525
588-525= 63 ft he is saving