Hi

let siraj be A

umesh be B

and udana be C

(A + B) 1 day work = 1/12,

(B + C) 1 day work = 1/15,

(C + A) 1 day work = 1/20

2(A+B+C) 1 day work = (1/12 + 1/15 + 1/20) = 12/60 = 1/5

(A+B+C) 1 day work = (1/2 * 1/5) = 1/10

working together they can complete the work in 10 days

A 1 day work = (1/10 - 1/15) = 1/30,

b 1 day work = (1/10 - 1/20) = 1/20

c 1 day work = (1/10 - 1/12) = 1/60

A alone can take the necessary steps in 30 days.

hope this information is helpful

Thank you.