When you have a right triangle, you can use the Pythagorean Theorem to find the missing side length. (but it only works for RIGHT triangles)
Pythagorean Theorem:
a² + b² = c² Since you know a=14 and b=7, plug it into the equation
(14)² + (7)² = c²
196 + 49 = c²
245 = c²
√245 = c or 15.6524758425 = c