phthagorean theorme is
a^2+b^2=c^2
where you have a right triangle and c =hypotonuse( normally the longest side, and opposite of right angle)
a and b are the legs
so we are given
one leg=8
hypotonues=10
subsitute
leg=a or b so just subsitute for one
subsitutt for b
a^2+8^2=10^2
expand
8^2=64
10^2=100
a^2+64=100
subtract 64 from both sides
a^2=36
square root both sides
a=6
answe ris 6 feet