Paul mixed 5 quarts of dry ingredients and 2 quarts of water to make a batch of concrete. he ran out of the mixture before finishing his project, so he made another batch using 15 quarts of dry ingredients

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.