As B moves 3 steps forward and then 1 step BACKWARD so in total 4 seconds he moves only 2 steps forward so in 116 seconds he moves 58 steps forward now in next 2 seconds he moves 2 steps so in 118 seconds he moves total 60 steps forward.

So no. of steps required to reach the top of the ESCALATOR is 60.

now LET d escalator moves a steps per second so in 4 seconds B moves 2 steps (3steps forward and 1 step backward)in these 4 sec. escalator moves 4a step so in 4 sec. B moves a total of 2+4a step.

so in 40 second total move=10*(2+4a)

so, 10*(2+4a) =60

hence a=1step/sec. 

As B moves 3 steps forward and then 1 step backward so in total 4 seconds he moves only 2 steps forward so in 116 seconds he moves 58 steps forward now in next 2 seconds he moves 2 steps so in 118 seconds he moves total 60 steps forward.

So no. of steps required to reach the top of the escalator is 60.

now let d escalator moves a steps per second so in 4 seconds B moves 2 steps (3steps forward and 1 step backward)in these 4 sec. escalator moves 4a step so in 4 sec. B moves a total of 2+4a step.

so in 40 second total move=10*(2+4a)

so, 10*(2+4a) =60

hence a=1step/sec.