Someone help me with this proof please

I'll give brainliest if you answer right : )

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

What percent of 18 is 24? and plz explain thx.