Problem: the length of the bridge , which a train 180 metres long and travelling at 45 km / hr can cross in 30 seconds , is ?
Rationale: "speed = [ 45 x 5 / 18 ] m / sec = [ 25 / 2 ] m / sec time = 30 sec let the length of bridge be x metres . then , ( 180 + x ) / 30 = 25 / 2 = > 2 ( 180 + x ) = 750 = > x = 195 m . answer : c"
annotated_formula: subtract(multiply(divide(multiply(45, speed(const_1000, const_1)), speed(const_3600, const_1)), 30), 180)