Answer : t = 0.75 second
Given that
[tex]\begin{gathered} y=-16t^2\text{ + 24t} \\ To\text{ calculate the number of time in seconds, we n}eed\text{ to differentiate y with t} \\ \text{ dy/dt = -2 }\cdot16t^{2-1}+1\cdot24t^{1-1} \\ \text{ dy/dt = -32t + 24} \\ \text{ let dy/dt = 0} \\ 0\text{ = -32t + 24} \\ 32t\text{ = 24} \\ \text{Divide both sides by 32} \\ t\text{ = }\frac{24}{32} \\ t\text{ = 0.75 second} \end{gathered}[/tex]