Answer:
Let's define the variables:
M = number of books that Marcus has.
x = number of books that Jessie has.
We know that:
"Marcus has one book less than three times the number of books that Jessie has."
Then the equation that represents the number of books that Marcus has is:
M = 3*x - 1.
Then if x tiles represent the number of books that Jessie has, the number of tiles for Marcus will be 3 times that, and then subtract one tile.
