A train overtakes two persons walking along a railway track. The first person walks at 4.5 km/hr and the other walks at 5.4 km/hr. The train needs 8.4 and 8.5 seconds respectively to overtake them. What is the speed of the train if both the persons are walking in the same direction as the train?  Choose the correct option:
A) 80 km/hr	B) 81 km/hr	C) 85 km/hr	D) 84 km/hr	E) 83 km/hr
Let x is the length of the train in meter and y is its speed in kmph   x/8.4 = (y-4.5)(10/36) ---(1)   x/8.5 = (y-5.4)(10/36) ---(2)   Dividing 1 by 2   8.5/8.4 = (y-4.5)/ (y-5.4)   =&gt; 8.4y - 8.4 × 4.5 = 8.5y - 8.5×5.4   .1y = 8.5×5.4 - 8.4×4.5   =&gt; .1y = 45.9-37.8= 
<gadget id="calculator">45.9-37.8</gadget>
<output>8.1</output>
8.1=&gt; y = 81 km/hr   Answer is 81 km/hr.
<result>B</result>
A train overtakes two persons walking along a railway track. The first person walks at 4.5 km/hr and the other walks at 5.4 km/hr. The train needs 8.4 and 8.5 seconds respectively to overtake them. What is the speed of the train if both the persons are walking in the same direction as the train?