The problem is asking you to find tha height of the ball after 0.75 seconds, and they give you the formula for the height:
![h(t)=-16t^2+10\text{ t + 6}](https://img.qammunity.org/2023/formulas/mathematics/college/54xlcptlp9az87zfkf7tlzm0zbdobd34rh.png)
So since this a function in terms of the time "t", all you need to do is to replace t with "0.75" in the equation, and thus obtain the height of the object at that moment in time:
![h(0.75)=-16(0.75)^2\text{+10 (0.75)+6=}4.5](https://img.qammunity.org/2023/formulas/mathematics/college/tpxoq1q8gn9qlrrqs41hh3q8bj4o5565yv.png)
The answer comes in feet, and it is: 4.5 ft