Answer:
The answer is 29 cm.
Step-by-step explanation:
The side we are looking for is the longest side of the right triangle, called a hypotenuse.
To find it, we first have to square 20, which equals 400. Then, square 21, which equals 441. Next, add 400 and 441 to make 841, then find the square root of 841, which is 29.
I hope this helped! :-)
