Basically its 250 + 16x = 210 + 18x where x = the number of hours doing the job.
Solving, we get 40 = 2x, x =20
The jobs has to be 20 hours long in order for their two painting jobs to be equally priced.
Hope this helped!
The formula is a permutation in which n represents the sample points in the set, while r represents the number of sample points in each permutation.
