13.288. A master and his apprentice were tasked with manufacturing a batch of identical parts. After the master worked for 7 hours and the apprentice for 4 hours, it turned out that they had completed $5 / 9$ of the entire work. After working together for another 4 hours, they found that $1 / 18$ of the entire work remained to be done. How long would it take the apprentice to complete the entire work on his own?