Earnings from a job are shared in proportion to the work done by each individual. If P works thrice as fast as Q, then their work ratio is 3:1. If P and Q together work four times as fast as R, then (P's work + Q's work) : R's work is 4:1. Combining these, if Q does 1 unit of work, P does 3 units. Together P and Q do 4 units. If P and Q's combined work (4 units) is 4 times R's work, then R does 1 unit of work. Thus, the ratio of work done by P, Q, and R is 3:1:1, and this is the ratio in which they should share earnings.