Let cost price of the product for the manufacturer be Rs. x.
Since, the manufacturer sells his product to the wholeseller at 20% return on cost.
But, this is the cost price for the wholeseller.
\(\therefore\) cost price for the wholeseller \(= Rs.\, \frac{6x}{5}\)
Now, wholeseller makes 20% profit on his cost price.
But, this is the cost price for the retailer.
\(\therefore\) cost price for the retailer \(=Rs.\,\frac{36x}{25}\)
Given retailer makes 28% margin on retail selling prices.
\(\therefore\) The percentage increase in the value of the product from the manufacturer to the consumer is 84.32%.