1. (4,0)
2. Yes. 1.6 and 2.0 match up on the line
3. Yes. 2.0 and 2.4 (same as above)
4. Yes. 8.0 and 10 (same)
5. divide number by 10/100/1000 and check whether they meet the points on the line.
I have no idea if I make any sense, but just ask if you have any more questions!