Hans wanted to find the length of the hypotenuse of the triangle. Which statement correctly identifies his error?

A right triangle has side lengths 40 centimeters and 9 centimeters. The hypotenuse is labeled c.

9 squared + 40 squared = c squared. 81 + 80 = c squared. 161 = c squared. StartRoot 161 EndRoot centimeters = c.
He did not square 40, he just multiplied by 2.
He did not finish the problem. He should have divided 161 by 2 to find the square root.
He should have added 9 + 9 to find the value of 9 squared.
He should have subtracted the two squares to get 40 squared minus 9 squared = c squared because numbers get too large if both legs are squared and then added together.