Let's use d as the variable name for the one-way distance. The flight's first phase consumed time t_1 flying at 240 km/hr and time t_2 flying at 320 km/hr. The total of those 2 time periods is
t_"total" = t_1 + t_2 = 35 cancel("minutes")*((1 hr)/(60 cancel("minutes"))) = 0.583 hrs
We need expressions for t_1 and t_2.
t_1 = d/(240 "km"/"hr")" " and " "t_2 = d/(320 "km"/"hr")
Going back to the equation for t_"total", we will put in the above expressions for the 2 time periods.
t_"total" = t_1 + t_2 = d/(240 "km"/"hr")" "+ " "d/(320 "km"/"hr")= 0.583 hrs
Now, a bunch of algebra ...
0.004167 "hr"/"km"*d" "+ " "0.003125 "hr"/"km"*d = 0.583 hrs
0.007292 "hr"/"km"*d = 0.583 hrs
d = (0.583 "hrs")/(0.007292 "hr"/"km") = 79.95 km
I hope this helps,
Steve
