what number would it be if it was on the first of three lines between 4 and 5

If the number is on the first line between 4 and 5, it would be closer to 4. Therefore, it would be a number slightly greater than 4 but less than 4.5.

what would the fraction be

The fraction between 4 and 5 that is closest to 4 would be 4 1/3, since it is slightly greater than 4.