1月24号考试！！！数学各种疑问！！跪谢亲们！！求解答啊！！

小晨会幸福

1月24号考试！！数学各种疑问！！！跪谢亲们啊！！！！ 亲们！！1月24号考试，数学还有很多疑问的伤不起啊！！！麻烦大家帮我解答解答吧！！谢谢大家了！！！祝愿大家全部700+啊！！！
1、In the xy-plane,what is the y-intercept of line l?
(1)The slope of line l is 3 times its y-intercept
(2)The x-intercept of line l is -1/3    答案E
我是怎么算都觉得应该是C啊！！  设 y=ax+b 则（1）a=3b (2) -1/a=-1/3  不就求出b了吗？？？

2、At a diner party,5 people are to be seated around a circular table.Two seating arrangements are considered different only when the positions of the people are different relative to each other.What is the total number of different seating arrangements for the group?答案是24  
这道题我直接看不懂啊！！麻烦详解！！跪谢！