Since it is a right triangle we can apply the Pythagorean theorem:
c^2 = a^2 + b^2
Where:
c= hypotenuse (the longest side) = 19
a & b = the other 2 legs of the triangle
Replacing:
19^2 = 10^2 + x^2
Solve for x
361 = 100 + x^2
361 - 100 = x^2
261 = x^2
√261 =x
x= 16.16