Answer: if you are referring to a right triangle the third side might be 20.5cm
Explanation:
I just used Pythagorean theorem in which c^2=a^2+b^2
so this is c^2= 225 + 196 and then you get c^2= 421 and finally you get the square root of 421 so this way you finally get 20.5 cm
Hope I helped
Pdt: a=15 b=14