X and Y are two station which are 320 miles apart. A train starts at a certain time from X and travels towards Y at 70mph. After 2 hours, another train starts from Y and travels towards X at 20mph. What time do they meet?

Question

$\begin{array}{11} (a)\; \text{5 hours } \\ (b)\;\text{6 hours} \\ (c)\; \text{8 hours } \\ (d)\; \text{4 hours } \end{array}$