Geno3141, I know you answered this, but I don't know how to do. Please help me. Thanks!

You need to know the location of the vertex, which is the highest point.

Your expression, -25t² + 75t + 24  has the form  at² + bt + c,  so  a = -25,  b = 75,  and  c = 24.

The x-vaue of the vertex can be found by using this little formula:  x-value  =  -b/(2a).

For this problem, the x-value of the vertex is  -75/(2·-25)  =  -75/-50  =  1.5

This represents the time of the maximum height; time = 1.5.

so, at what time is the height of the ball at its maximim? Sorry i need this quick

wait, is the time 1.5? Is that the answer?

the time is 1.5  (probably seconds, but that isn't specified).

thank you so much!