The selling price, s, of an item is s = c + mc, where c is the cost of the item and m is the percent markup based on cost. what is the formula solved for m?

At a pizza shop 70% of the customers order a pizza 25% of the customers order a salad and 15% of the customers order both a pizza and a salad if s customer is chosen at random what is the probability that he or she orders either a pizza or a salad