Lilet can do a certain job in 8 hours and her daughter krizia can do it in 10 hours. After the two nave been working together for 3 hours, they were joined by katrin and they completed the job in 1 more hour. How long will it take katrin to do the same job by herself?

3[1/8 + 1/10] = 27/40

     13/40 = 1/8 + 1/10 + 1/x

1/x = 4/40

x = 10 days