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Starting homework at 12 PM and Taking a break at 3:30 PM,

we came to know that each of them have already spent

3 hrs and 30 minute i.e 210 min

After taking break, they started to do their homework at 4 PM

1. Rajesh can finish 1/5 of his work in 1 hr. i.e in 60 min

He can finish 1 work in 60* 5 = 300 min

Remaining time to complete his hm work = 300-210= 90 min

Starting again at 4 PM,he will finish his homework at 5:30 PM

2. Sema can finish 3/7 of her homework in 90 min

She will finish 1 work in 90*(7/3) = 210 min

Therefore she finished her work at 3:30 PM

3.

Ramya can finish 3/4 of her work in 210 min

She will finish 1 work in 210*(4/3 ) min= 280 min

Remaining time left for Ramya to complete her work =280 - 210 = 70 min

Starting to do homework again at 4 PM, she will complete her work at 5:10 PM

Since Rajesh takes a longer time to finish the work (completing the work at 5:30 PM), hence they all can start to play at 5:30 PM. That\'s the only time they all will meet