Answer: The incremental income on reworking the units is $17,280.
The question asks us to compute incremental profit or loss on reworking defective units.
Hence the cost that has already been incurred in producing the defective units is not considered here.
The per unit incremental revenue we get by reworking the defective units is:
Incremental Revenue = (Revenue from selling reworked units) -
(Revenue from selling defective units)
Incremental Revenue (per unit) = $15.8 (20.60 - 4.80)
Incremental Cost of re-working a unit = $6.20
Incremental Income from re-working per unit = Incremental Revenue per unit -
Incremental Cost per unit
Incremental Income from reworking (per unit) = $9.60 (15.80 -6.20)
Total no. of defective units = 1,800
Total incremental income from reworking = $9.60 × 1,800 = $17,280.