Urgent! Please help number 14 with the working. Thank you.

Subject: Proportionality

Assuming that 5 men need x days to complete the job.
5 men => x days
(5 + 1) men => (x - 8) days
We get,
5 / (5 + 1) = (x - 8) / x
6x - 48 = 5x
x = 48.
Now, we must find how many men should be hired if we need to complete the job in 48 - 28 = 20 days.
5 men => 48 days
y men => 20 days
We get,
5 / y = 20 / 48
20y = 240
y = 12 
Hence, we need 12 men to do the job. In other words, we need 7 additional men to do it.