Can someone answer this fore real?

How many different ways can you make change for $.50 using only nickels,dimes, and quarters?

The volume of a cube is 8 in to the 3rd power. how long is each side?

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.