Solve the Problem $S$ (In Mph) of a Vehicle Traveling a Distance Of

Solve the problem.
-The average round trip speed $S$ (in mph) of a vehicle traveling a distance of $d$ miles in each direction is given by $\mathrm { S } = \frac { 2 d } { \frac { d } { r _ { 1 } } + \frac { d } { r _ { 2 } } }$ where $r _ { 1 }$ and $r _ { 2 }$ are the rates of speed for the initial trip and the return trip, respectively. Suppose a motorist travels 100 miles to an event and averages 50 mph for the trip to the event. Determine the average speed necessary for the return trip if the motorist wants the average
Speed for the round trip to be at least 60 mph. Round to one decimal place, if necessary.

A) The motorist must average a speed of at least 65 mph on the return trip.
B) The motorist must average a speed of at least 70 mph on the return trip.
C) The motorist must average a speed of at least 55 mph on the return trip.
D) The motorist must average a speed of at least 75.0 mph on the return trip.