SOMEONE HELP Pls and ty

How do you use the elimination method for this question? explain, because i really want to understand!

Saline iv fluid bags cost $64.20 for 24, 1000 ml bags from one supplier. a new supplier sells 500 ml bags for $2 each. the hospital uses about 10,000, 1000 ml bags each month. nurses report that about half of the bags are more than half full when they are discarded. if you are going to use only one supplier, which size bag provides the best deal, and how much will you save each month? compare the cost of the new supplier to the current one.

Look at this pattern ; 1,4,9, number 10000 belongs in this pattern . what’s the place of this number?