In both the figures we have a Right Angled Triangle.
Two sides of the right angled triangles are given and we are to find the Third side. This can be done using the Pythagoras Theorem, which states:
Hypotenuse² = Base² + Perpendicular²
For 1st figure, we have
Base = 21
Perpendicular = 20
So,
Hypotenuse² = 20² + 21² = 841
⇒
Hypotenuse = 29 (1st option is correct)
For 2nd Image, we have
Base= 6
Hypotenuse = 10
So, we can write:
10² = 6² + Perpendicular²
Perpendicular² = 64
⇒
Perpendicular = 8 (Option Fourth)