Answer:
Grace should use her phone for 58 minutes to maintain an average of 55 minutes.
Step-by-step explanation:
Usage of first month = 43 minutes
Second month = 62 minutes
Third Minutes = 57 minutes
Let, the usage of fourth month = k minutes
Mean of the data = 5 minutes
Now, Average of a Data = 
⇒
or, 55 x 4 = 162 + k
⇒ 220 - 162 = k
or, k = 58 minutes
So, Grace should use her phone for 58 minutes to maintain an average of 55 minutes.
check the picture below.
so, the rocket will come back to the ground when h(t) = 0, thus
![\bf h(t)=-3t^2+12t\implies \stackrel{h(t)}{0}=-3t^2+12t\implies 0=-3t(t-4)\\\\[-0.35em]~\dotfill\\\\0=-3t\implies 0=t\impliedby \textit{0 seconds when it took off from the ground}\\\\[-0.35em]~\dotfill\\\\0=t-4\implies 4=t\impliedby \textit{4 seconds later, it came back down}](https://tex.z-dn.net/?f=%5Cbf%20h%28t%29%3D-3t%5E2%2B12t%5Cimplies%20%5Cstackrel%7Bh%28t%29%7D%7B0%7D%3D-3t%5E2%2B12t%5Cimplies%200%3D-3t%28t-4%29%5C%5C%5C%5C%5B-0.35em%5D~%5Cdotfill%5C%5C%5C%5C0%3D-3t%5Cimplies%200%3Dt%5Cimpliedby%20%5Ctextit%7B0%20seconds%20when%20it%20took%20off%20from%20the%20ground%7D%5C%5C%5C%5C%5B-0.35em%5D~%5Cdotfill%5C%5C%5C%5C0%3Dt-4%5Cimplies%204%3Dt%5Cimpliedby%20%5Ctextit%7B4%20seconds%20later%2C%20it%20came%20back%20down%7D)
Answer:
53
Step-by-step explanation:
90 degrees in a right angle.