Working together, Sam and Charlie can change all the light bulbs in the office building in 3 hours. It would have taken Charlie 8 hours to do the job alone. A table showing Rate in part per hour, Time in hours, and Part of Light Bulbs Changed. The first row shows, Sam, and has r, 3, and r times 3. The second row shows Charlie, and has StartFraction 1 Over 8 EndFraction, 3 and StartFraction 1 Over 8 EndFraction times 3.
Which equation can be used to solve for the rate, r, for Sam to change all the light bulbs in the office building by himself?

3r = 3 r equals StartFraction 3 Over 8 EndFraction.
3r + 3 r plus StartFraction 3 Over 8 EndFraction equals 1. = 1
r + StartFraction 1 Over 3 EndFraction r plus StartFraction 3 Over 8 EndFraction r equals 1.r = 1
r + StartFraction 1 Over 3 EndFraction r plus StartFraction 1 Over 8 EndFraction r equals 1.r = 1