A density curve for all the possible temperatures between 0°F and 20°F is a rectangle. What is the height of the rectangle in this density curve?

Any is very appreciated! (picture is provided below)not sure how to do this at all won't lie

The chs baseball team was on the field and the batter popped the ball up. the equation b(t)=80t-16•16+3.5 represents the height of the ball above the ground in feet as a function of time in seconds. how long will the catcher have to get in position to catch the ball before it hits the ground? round to the nearest second

Could somebody me with this radical simplification?