13.138. Two workers, the second of whom started working 1.5 days later than the first, independently wallpapered several rooms in 7 days, counting from the moment the first worker started. If this work had been assigned to each separately, the first would have needed 3 days more than the second to complete it. How many days would each of them take to complete the same work individually?
Solution.

Let the first worker complete the entire job in $x$ days, the second in $x-3$ days. In 7 days, the first worker completed $\frac{7}{x}$ of the entire job, and in $7-1.5=5.5$ days, the second worker completed $\frac{5.5}{x-3}$ of the job. Therefore, $\frac{7}{x}+\frac{5.5}{x-3}=1$, from which $x=14$ days.

Answer: in 14 and 11 days.