We are given that an object falls with an acceleration of -6 miles/h/s. To determine the initial velocity we will use the following motion:
![v_f=v_0+at](https://img.qammunity.org/2023/formulas/physics/college/qgre38q8sgm0h17jd2cw9z9w3fnmh5ftbi.png)
Where:
![\begin{gathered} v_f,v_0=\text{ final and initial velocity} \\ a=\text{ acceleration} \\ t=\text{ time} \end{gathered}](https://img.qammunity.org/2023/formulas/physics/high-school/4ts2t1ot77rc5u45zi269fzepep059djm2.png)
Now, we solve for the initial velocity by subtracting "at" from both sides:
![v_f-at=v_0](https://img.qammunity.org/2023/formulas/physics/high-school/whg8vbv2ec89txeqsmls03gwoxecst48oj.png)
Now, we plug in the values:
![80(mi)/(h)-(6(mi)/(hs))(5s)=v_0](https://img.qammunity.org/2023/formulas/physics/high-school/h05me535rcfbligidrpbpn4s6sorkt41kv.png)
Now, we solve the operations:
![50(mi)/(h)=v_0](https://img.qammunity.org/2023/formulas/physics/high-school/qtylehthlv7mqn98m22t1e6uejuey6ynk7.png)
Therefore, the initial velocity is 50 mi/h.