Help

You have to multiply the number of rails by 29.

An easy way of doing this is to multiply by 30 and then subtract the number of rails.

Examples:

2 x 29 is the same as 2 x 30 - 2

3 x 29 is the same as 3 x 30 - 3

4 x 29 is the same as 4 x 30 - 4