Algebra 1 · Challenge problem

Two cars travel along a straight highway marked with mile markers. At time $t=0$ hours, car A is at marker $5$ and moves toward increasing markers at $6$ mph; car B is at marker $65$ and moves toward decreasing markers at $2$ mph. Find the sum of all values of $t \ge 0$ (in hours) at which the cars are exactly $12$ miles apart.