We know that
• From A to B the speed is 13 miles per hour.
,• From B to C the speed is 12 miles per hour.
,• The total distance is 75 miles.
We have to use the following formula
[tex]\begin{gathered} T_t=\frac{2\cdot D_t}{v_1+v_2} \\ T_t=\frac{2\cdot75}{13+12} \\ T_t=\frac{150}{25} \\ T_t=6 \end{gathered}[/tex]