Answer:
x = (66.50 - 4y) / 3
Explanation:
Given that:
Amount had = $70
Change collected = $3.50
Total amount spent = $(70 - 3.50) = $66.50
Total amount used for purchasing prawn and fish:
Kg of fish = 4
Kg of prawn = 3
1 kg prawn will cost, x
If 1 kg of fish = y
(Total amount spent - cost of 4 kg fish) / Number of kg of prawn
($66.50 - 4y) / 3
x = (66.50 - 4y) / 3