Physics: Finding tension and normal force in an inclined plane

The metric unit of electrical power is the watt volt ampere ohm

From center station, a train departs every 30 minutes on the fast line and a train departs every 50 minutes on the state line. if two trains depart from center station at 8: 00 a.m., one on each of the two lines, what is the next time that two trains, one on each line, will depart at the same time?

Which best represents the law of conservation of mass ?