Answer :
Answer: 60 mph
Step-by-step explanation:
Given
The red car left at 9 am and arrives at 1 pm
time taken by the red car [tex]t_a=4\ hr[/tex]
time taken by the blue car [tex]t_b=3\ hr[/tex]
Assume the speed of the red car is v
So, the speed of the blue car is v+15
distance traveled by them is the same
[tex]\Rightarrow v\times 4=(v+15)\times 3\\\Rightarrow 4v=3v+45\\\Rightarrow v=45\ mph[/tex]
Thus, the speed of the blue car is [tex]45+15=60\ mph[/tex]