20 workers per day work = 1/30

x/30 + 15 workers per day work * (35-x)= 1

(x + 1050 * 15 workers per day work - 30 * 15 workers per day work * x ) /30 =1

x +15 workers per day work * (1050 - 30x) = 30

**What is the per day work of 15 workers =**

per day work of 20 workers= 1/30

per day work of 1worker = 1/(30 * 20)= 1/60

per day work of 15 workers = 15 * 1/60 = 0.25 ?