A 3-gallon jug of water costs $16.80. What is the price per cup?

Can someone explain the elimination method to me for this problem?

School has 204 sixth grade students. if the sixth grade is 30% of the total school, how many students are in the middle school?

Problem situation: caren is making rice and beans. she can spend no more than $10 on ingredients. she buys one bag of rice for $4.99. beans cost $0.74 per pound. how many pounds of beans, x, can she buy? inequality that represents this situation: 10≥4.99+0.74x drag each number to show if it is a solution to both the inequality and the problem situation, to the inequality only, or if it is not a solution.