"if peter had 400 stamps 5/8 of them are singapore stamps and the rest were us stamps he gave 1/5 of the singapore stamps to a friend. how many stamps were left"

Zahra was given two data sets, one without an outlier and one with an outlier. data without an outlier: 15, 19, 22, 26, 29 data with an outlier: 15, 19, 22, 26, 29, 81

You paid 28.00 for 8 gallons of gasoline. how much would you pay for 15 gallons of gasoline?

Offering 30 if a plus b plus c equals 68 and ab plus bc plus ca equals 1121, where a, b, and c are all prime numbers, find the value of abc. the answer is 1978 but i need an explanation on how to get that.