To calculate the cost of Irish butter per 100g, we can divide the cost of the tub by its weight in grams and then multiply by 100.
The cost per 100g of Irish butter is given by the equation:
cost per 100g = (cost of tub / weight of tub) * 100
Substituting the given values, we get:
cost per 100g = (2.80$ / 350g) * 100
Solving this equation, we find that the cost of Irish butter per 100g is:
cost per 100g = 0.80$ / 100g
So the cost of Irish butter per 100g is 0.80$.