We Have,
Working days of A = 24 days
Working days of B = 30 days
Working days of C = 40 days
Then,
`=>` 1 days work of `A , B & C = 1/24 + 1/30 + 1/40`
`=>` 1 days work of `A , B & C = ( 5 + 4 + 3)/120`
`=>` 1 days work of `A , B & C = 12/120`
`=>` 1 days work of `A , B & C = 1/10`
According to question,
C left 4 days of before completion of work .
Thats means only A & B work during the last 4 days .
So,
`=>` Work done by A & B during the last 4 days = `4(1/24 + 1/30)`
`=>` Work done by A & B during the last 4 days = `4(5+4)/120`
`=>` Work done by A & B during the last 4 days = `4 × 9/120`
`=>` Work done by A & B during the last 4 days = `3/10`
So,
Remaining Work = 7/10,
which was done by A,B and C in the initial number of days.
And,
==> Number of days required for this initial work = 7 days.
Thus,
The total numbers of days required = 4 + 7 = 11 days.
Hence
Required number of days will be = 11 days.
