Presented below is selected information for three regional divisions of Medina Company.

Divisions
North West South
Contribution margin $299,200 $499,600 $400,900
Controllable margin $139,500 $360,000 $211,500
Average operating assets $930,000 $2,000,000 $1,410,000
Minimum rate of return 12% 14% 9%

Required:
a. Compute the return on investment for each division.
b. Compute the residual income for each division.