Leaving the house at 2:30 pm, Cayson reaches his destination in 2.5 hours i.e at 5 pm.
Leaving the house at the same time, Riley reaches his destination in 3 hours i.e 5:30 pm
Both the destinations are opposite to each other and are 385 miles apart.
Total time taken by both the brothers is equal to 3 + 2.5 = 5.5 hours
We know,

Speed =

Speed of both the brothers is 70 miles per hour.... Answer