The missing side has a length of 10.2m rounded to the nearest 10th.

The Pythagorean Theorem states for a right triangle as given:

##a^2 + b^2 = c^2## where ##a## and ##b## are the sides and ##c## is the hypotenuse.

In this problem ##a## and ##c## have been provided so we can substitute for these and solve for ##b## while keeping the equation balanced:

##11^2 + b^2 = 15^2##

##121 + b^2 = 225##

##121 + b^2 – 121 = 225 – 121##

##b^2 = 104##

##sqrt(b^2) = sqrt(104)##

##b = 10.2## rounded to the nearest 10th.