Answer:
1) 1.1 seconds
2) 13.5 feet
Part A
[tex]\rightarrow \sf -16t^2 + 5t + 15 = 0[/tex]
Apply quadratic formula:
[tex]\rightarrow \sf t= \dfrac{-5\pm \sqrt{5^2-4\left(-16\right)\cdot \:15}}{2\left(-16\right)}[/tex]
Simplify following
[tex]\rightarrow \sf t=-\dfrac{-5+\sqrt{985}}{32},\:t=\dfrac{5+\sqrt{985}}{32}[/tex]
In decimal form:
[tex]\rightarrow \sf t=-0.825 ,\:t=1.137[/tex]
Conclusion:
As time is be only positive: t = 1.1 seconds
Part B
[tex]\rightarrow \sf h=-16t^2 + 5t + 15[/tex]
insert t = 0.5
[tex]\rightarrow \sf h=-16(0.5)^2 + 5(0.5) + 15[/tex]
simplify
[tex]\rightarrow \sf h=13.5[/tex]
