Alright, lets get started.
If Matthew wants to complete packages at an average rate of at least 39 packages per hour.
And they worked 4 hrs only due to picnic, yesterday, it means they have to make packages.
But they made only 112 packages means they are short of packages.
Suppose they are working today t hrs, and his department will complete 43 packages per hour today.
It means they are going to make 43 t packages today.
This 43 t packages includes those 44 too , which they are short of yesterday due to picnic.
So, average will be
(39 average given in question)
Cross multiplying
Adding 44 in both sides
Subtracting 39 t in both sides
Dividing 4 in both sides
t = 11 hrs
Hence they have to woth 11 hrs today : Answer
Hope it will help :)