Answer :
Solution
For this case we can create the following schema
We can use the definition of distance:
x= vt
We can find the relative velocity:
[tex]V_{\text{rel}}=4-2=2\frac{mi}{hr}[/tex]And the distance between both is required to be 2 mi so then we can find the time like this:
[tex]t=\frac{x}{v_{\text{rel}}}=\frac{2mi}{\frac{2mi}{hr}}=1hr[/tex]Then the answer is:
1 hr
