George rides his bike 9km south and then 12 km east. how far is he from his staring point?

When George was finished riding south and he turned east,
he turned 90 degrees.  Right there, he made his whole trip
into a right triangle !

The 'legs' of the triangle are his 9km piece and his 12 km piece.
At the end of that much travel, his distance from his staring point
is the hypotenuse of the right triangle.

You know that the length of the hypotenuse is the square root of

        (the length of one leg)² plus (the length of the other leg)²

So his distance from the staring point is

                         √ (9² + 12²)  km .

I'm pretty sure that you can pick it up and carry it up from here.