Bought: 350 × $80 = $28,000

Sold:

175 × $192.00 = $33,600

152 × ($192.00)×(1-(1/3)) = 152 × $192×(2/3) = 152 × $128 = $19,456

(350-175-152) × $75.00 = 23 × $75.00 = $1,725

Total Sold = $54,781

a) What was the average rate of markup?

OK, here we need to define what markup is. I think of it as price vs marginal cost ... in other words excluding overheads:

Average rate of Markup = $54,781 / $28,000 = 1.956 = 196% (markup is usually expressed as a percentage)

[ If you must include overheads you would increase the cost base by 50%. $28,000 plus 50% = $28,000 × 150% = $42,000, and the markup would be: $54,781 / $42,000 = 1.304 = 130% ]

Total cost per month:

Easiest way is to determine cost per unit: $80 plus 50% = $80 × 150% = $120

175 × $120 = $21,000

152 × $120 = $18,240

23 × $120 = $2,760