a train speeds past a pole in 15 sec and a platform 140 m long in 25 sec , its length is ?
"let the length of the train be x m and its speed be y m / sec . then , x / y = 15 = > y = x / 15 ( x + 140 ) / 25 = x / 15 = > x = 210 m . answer : d"
multiply(140, subtract(const_2, const_1))