I found a similar problem. It had an accompanying mural box. It is 18 by 18.
Area = 18 * 18 = 324 square units
Riley agreed to prepare 1/2 of the area = 324 square units * 1/2 = 162 square units.
Morgan agreed to clean and seal 1/3 of the area = 324 square units * 1/3 = 108 square units
Reggie agreed to finish the work on the remaining 1/6 of the area = 324 square units * 1/6 = 54 square units.
Riley completed 1/3 of his part = 162 square units * 1/3 = 54 square units
Morgan completed 5/6 of her part = 108 square units * 5/6 = 90 square units
Reggie completed 2/3 of his part = 54 square units * 2/3 = 36 square units
Completed the most mural: Morgan
Completed the least mural: Reggie