Question 586263
Actually, the answer is 9 inches.

The Pythagorean Theorem tells us that for a right triangle with sides of length a and b hypotenuse of length c, {{{a^2 + b^2 = c^2}}}
We're given one side (one foot = 12 inches) and the hypotenuse (15 inches).  So plugging these values into the Pythagorean Theorem gives:
{{{12^2 + b^2 = 15^2}}}
{{{144 + b^2 = 225}}}
{{{144 + b^2 - 144 = 225 - 144}}}
{{{b^2 = 81}}}
{{{b = 9}}}
The other side of the right triangle is 9 inches.