There were 640 T-shirts at a stall. ⁵₈ of them were with collars. T-shirts with collars were priced at $5 each. T-shirts without collars were priced at $10 each. The stall owner sold ⁴₅ of the T-shirts with collars and ⁴₅ of the T-shirts without collars. How much did he collect from all the T-shirts he sold?
Number of T-shirts = 8 u

8 u = 640

1 u = 640 ÷ 8 = 80

Number of T-shirts with collars
= 5 u
= 5 x 80
= 400

Number of T-shirts with collars sold 
= ⁴₅ x 400
= 320

Number of T-shirts without collars
= 3 u
= 3 x 80
= 240

Number of T-shirts without collars sold
= ⁴₅ x 240
= 192

Amount that the stall owner collected from the sale of the T-shirts with collars
= 320 x 5
= $1600

Amount that the stall owner collected from the sale of the T-shirts without collars
= 192 x 10
= $1920

Total amount that the stall owner collected from all the T-shirts he sold
= 1600 + 1920
= $3520

Answer(s): $3520