28 men can finish the job in 60 days. at the start of the 16 day, 5 men were laid off and after the 45th, 10 more men were hired. how many days were delayed in finishing the job? explain, step by step.

Every day one man can do 1 / ( 28* 60 ) = 1 / 1620 of a job.
After 15 days: 
( 28 * 15 ) / 1620 = 1 / 4
From the 16 th to the 45 th day:
( 23 * 30 ) / 1620 = 23 / 56
1 /4 + 23 / 56 + ( 33 * x ) / 1620 = 1
14 / 56 + 23 / 56 + 11 x / 560 = 1
140/ 560 + 230 / 560 + 11 x / 560 = 1
370 + 11 x = 560
11 x = 190
x = 190 : 11 ≈ 17.27
17.27 - 15 = 2.27 days
3 days were delayed in finishing the job. 

Do you need with the x value for the minimum? its always between the two intercepts for a parabola