C: 8 cm
Assuming no friction, since the ball is starting with an elevation of 20 cm, it will end up with an elevation of 20 cm. So let's just calculate the result.
"slope of 5 cm of rise for each 2 cm of run". So for every 5 cm the ball rises, it will go 2 cm horizontally. Since we know the ball will have a total rise of 20 cm, that gives us
20 cm / 5 cm * 2 cm = 8 cm
And looking at the available answers, 8 cm is sitting right there. So the answer is
C: 8 cm
