Richard went to a zip line park for his birthday. Richard travels on the zip line at a constant rate. The points on the following coordinate plane show how many feet he travelled in 222, 333, and 444 seconds while riding one of the zip lines.

How far does Richard travel on the zip line in 111 second?

answer: b.

step-by-step explanation:

the y coordinate for point b is 0, and answer b is the only one with that y coordinate.

there is only one way to arrange all the eight relative to each other because they are not distinct. we have

now there are nine places to place an (and not more than one in one place).   because we have four symbols, we need to choose four of these nine places to insert an . order does not matter because the are not distinct.

thus there are 1 · c(9,4) ways, or, if we calculate it,

thus there are 126 ways to form such "words."