Two trains are each 50 m long moving parallel towards each other at speeds \[10\text{ }m/s\] and 15 m/s respectively. After what time will they pass each other?

• A. \[5\sqrt{\frac{2}{3}}sec\]        
• B. \[4\text{ }sec\]
• C. \[\text{2 }sec\]              
• D. \[\text{6 }sec\]