Bob can shingle 1 roof for every 10 hours of work. (1/10)James can shingle 1 roof for every 16 hours of work. (1/16)To find out what they can do together, you must add their rates of work together.This will be the number to find how fast they can shingle 1 roof in t amount of hours (1/t) 1/10 + 1/16 = 1/t 8/80 + 5/80 = 1/t 13/80 = 1/t Cross multiply 13(t) = 1(80) 13t = 80 t = 6.15 It would take them 6.15 hours to complete the roof together.