From the following particulars, work out the earnings for the week of a worker under (a) straight piece rate system, (b) differential piece rate system, (c) Halsey’s premium system and (d) Rowan’s system:

Number of working hours per week: 48

Wages per hour: Rs 3.75

Normal time per piece: 20 minutes

Rate per piece: Rs 1.50

Normal output per week: 120 pieces

Actual output for the week: 150 pieces

Differential piece rate: 80% of piece rate when output is below standard and 120% when output is above standard.