Ariel, Bianca, and Camila are spray painting. Ariel could do it all by herself in $12$ hours, and Bianca could do it all by herself in $10$ hours. Ariel and Bianca work together for $3$ hours, then Camila joins in. The job finishes in another $2$ hours. How many hours would it take for Camila to do all the spray painting by herself?
Find the time for A and B together:
1 / (1 / A + 1/B) = T
T = 60/11 = 5.55
they work for 3 hours ....this leaves (4.55 - 3) / 5,55 job left = 0.4499625031247395967
Now all three work together and take two hours to complete the fraction of a job that is left:
.4499 / ( 1/12 + 1/10 + 1/c) = 2
c = 24 hours
