Answer: I used the Pythagorean theorem and got 6.24, but if I was supposed to use another method, just let me know.
The formula is a^2+b^2=c^2
a=5
c=8
b=?
5^2+b^2=8^2
25+b^2=64
b^2=39
b=6.24,
(If it doesn't work, put x=6.24, x=-6.24. It can be both technically, but most teachers ask only for the first one. )
