Prakash and Vikram can do a work in 6 hours. Vikram alone can do it in 8 hours. How long will Prakash take to do it alone?

V = 1 job/ 8 hr

P = 1 Job / x hr
1 job = (1/8 + 1/x) * 6 hr
1/8 + 1/x = 1/6
6 x + 48 = 8 x
2 x = 48
x = 24 hours
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Check
in an hour together do
1/24 + 1/8 = 4/24 = 1/6 sure enough