GMAT OG12 problem solving的几道题

GMAT OG12 problem solving的几道题
P274 14题这句话看太不懂：Car X drove onto the bridge exactly 3 seconds after Car Y drove onto the bridge and drove off the bridge exactly 2 seconds after Y drove off the bridge.
P274 18题what is the maximum number of rectangular blocks,each with dimensions 12 centimeters by 6 centimeters by 4 centimeters,that will fit inside rectangular Box
(1)when Box X is filled with the blocks and rests on a certain side,there are 25 blocks in the bottom layer.说实话书后面这个(1)的答案我看得不太懂,你们能不能帮我看看啊!
P274 23题 the profit from the sale of a certain applicance increases,though not proportionally,with the number of units sold.did the profit exceed $4 million on sales of 380,000 units?
(1)The profit exceed $2 million on sales of 200,000 units.
(2)The profit exceed $5 million on sales of 350,000 units.
P279第70题 Mary persuaded n friends to donate $500 each to her election campaign,and then each of these n friends persuaded n more people to donate $500 each to Mary's campagin.If on one donated more than once and if there were no other donations,what was the value of
答案(2)中 500（n的平方+n）=120000
这个n的平方怎么算的,