to solve this you would use pythagorean theorm which is a^2+b^2=c^2.
The hyotenuse is obviouly 11 and one of the side lengths is 4 so you would put 4^2+b^2=11^2 which is 16+b^2=121. You subtract 16 to get b^2 = 105 and then square root both sides, So the answer would be √105.