The hypotenuse of a right triangle is twice the length of one of its legs. th length of the other leg is three feet. find the lengths of three sides (in feet).

Let
x> the length side of the hypotenuse
y> the length side of the unknown leg

we know that
x=2*y> equation 1
applying the Pythagoras Theorem
x²=y²+3²> equation 2

substitute equation 1 in equation 2
[2*y]²=y²+3²> 4*y²-y²=9> 3*y²=9> y²=3
y=√3 ft
x=2*y> x=2*√3 ft

the answer is
the lengths of the three sides are
hypotenuse=2√3 ft
one leg=√3 ft
other leg=3 ft