Working together, Rocco and Giulia can paint a room in 3 hours. It would have taken Rocco 7 hours to do the job alone. Which equation can be used to determine r, Giulia’s rate of work in parts per hour?
1/r + 1/ g = 1/3
1/7 + 1/g = 1/3 solve for g, Gulia's rate
1/g = 1/3 - 1/7
1/g = 4/21
g = 21/4 hr