Can someone please help me <3

How many $20 bills do you need to have to make $280

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.

Hardest math question of all time can you solve the equation. check for extraneous solutions.9∣9-8x∣ = 2x+3