Answer:
0.5hrs
Step-by-step explanation:
Let the speed downhill be [tex]x[/tex],
Speed uphill is [tex]0.5x[/tex]. We are told than speed uphill is [tex]\frac{2}{3}[/tex] the speed on flat ground. Therefore the speed on level ground will be [tex]\frac{0.5x}{2/3}=0.75x[/tex].
From this info, we can obtain the actual speed,[tex]v_g[/tex] on level ground as:
[tex]x=120m/h\\0.75x=v_g\\\\\therefore v_g=\frac{0.75x \times 120m/h}{x}\\v_g=90m/h[/tex]
speed, distance and time have the relation [tex]s=d/t[/tex] so to obtain time to cover 45miles:
[tex]t=d/s\\=45/90\\=0.5h[/tex]
Hence it takes 0.5hrs to cover 45miles on flat ground.
