Find the probability that event a will appear at least three times in four independent tests if the probability of occurrence of event a in one test equal to 0.4

This kind of problems are solved using Bernoulli's distribution. Everytime you have a win/lose scenario, and you know the probability of winning, and you want successes over trials, you have the following probability:

You want the probability of having at least three successes, i.e. you are interested in the cases k=3 and k=4. The corresponding probabilities are

So, the total probability is

b, i believe, but not sure.

if you're trying to figure out how much each ounce cost it would be 0.20

cents each ounce