Answer:
64
Step-by-step explanation:
Euclide's theorem states that in a right triangle, the square built of the side lenght is equivalent of the rectangle with sides hypotenuse and projection of the same side lenght. In formula, given the measures on the triangle:

One decimeter equals 10 centimeters. So 3 decimeters equals 30 centimeters. They are equal.
The first column is meters and the second column is centimeters. =)
The second one, 69/24 = 23/8 and cannot be simplified further