Graphing inequalities

How is working backward similar to solving an equation?

Which expression do you get when you eliminate the negative exponents of 4a^2 b^216a^-3 b

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