3 persons undertake to complete a piece of work for $1,200. The first person can complete the work in 8 days, second person in 12 days and third person in 16 days. They complete the work with the help of a fourth person in 3 days. What does the fourth person get?

Work done by (P + Q) = 7/22
Work done by R = 1 - (7/ 22) = (22-7)/22 = 15/22
? (P + Q)'s share : R's share = (7/22) : (15/22) = 7 : 15
R's share = (15/22) x 1100 = 15 x 50 = ? 750

It is required to find the highest common factor of 5750 and 5000, because his daily wage is their common factor.
Hence, the daily wage is ? 250.

A can do a work in 12 days.
? Work done by A = 1/12
B can do a work in 16 days.
? Work done by A = 1/16
Ration of Work done by A : Ration of Work done by B = 1/12 : 1/16
Ration of Work done by A : Ration of Work done by B = 4 : 3
A's shares = 2100 x 4/7 = 300 x 4 = ? 1200
B's share = 2100 x 3/7 = 300 x 3 = ? 900

A, B and C contract to do a work for ? 4200. A can do the work in 6 days, B in 10 days and C in 12 days.
From given question, As we know that
A can do the work in 6 days.
A can do 1/6 work in one day.
B can do the same work in 10 days.
B can do 1/10 work in one day.
C can do the same work in 12 days.
C can do 1/12 work in one day.
Work done shared by A : B : C = 1/6 : 1/10 : 1/12
Multiply by 60, we will get,
Work done shared by A : B : C = 10 : 6 : 5
Let us assume ration variable is P.
According to question,
10P + 6P + 5P = 4200
? 21P = 4200
? P = 200
A's share = 10P = 10 x 200 = ? 2000
B's share = 6P = 6 x 200 = ? 1200,
C's share = 5P = 5 x 200 = ? 1000