Since the triangle is a right angled triangle, Pythagoras Theorem must be satisfied.
From the diagram, it is observed that 'c' is the hypotenuse, and 'a' and 'b' are the legs.
Then the Pythagoras Theorem becomes,
Substitute the given values,
Taking square roots on both sides of the equation,
Note that we have neglected the negative value '-20' for 'b' since the side of a triangle cannot be negative.
Thus, the side 'b' is 20 inches.