We have two trains that leave Mexico City at the same time, one to the east and the other to the west. The train that travels to the west is 10 mph slower than the other train. The diagram of the problem is:
The combined velocity is:
[tex]V_T=v+v-4=2v-4[/tex]
The equation that relates the distance D between the trains and the time after t hours is:
[tex]D=V_T\cdot t[/tex]
If after 1.5 hours the trains are 171 miles apart, then using the equation above:
[tex]\begin{gathered} 171=V_T\cdot1.5 \\ V_T=\frac{171}{1.5} \\ V_T=114 \\ 2v-4=114 \\ 2v=118 \\ v=59\text{ mph} \end{gathered}[/tex]
Now, the speeds are:
[tex]\begin{gathered} \text{East}\colon59\text{ mph} \\ \text{West}\colon55\text{ mph} \end{gathered}[/tex]
