Answer:
The Pythagorean Theorem states that A^2+B^2=C^2
Side A=58
Side B=?
Side C=42
Plug those in to up above
58^2+B^2=42^2
3364+b^2=1764
B^2= -1600
Square root both sides to get:
B= 40i
It would be 40i because you had a negative when trying to square root.
Hope this helps ;)