CUSING TOOLS Use the unit fraction $\frac{1}{5}$ to represent the space between the tick marks on the number line. Write an expression involving subtraction that is being modeled. Then find the difference. A number line with two arrows on top of it. It has four tick marks to the left of 0 and two tick marks to the right of 0. One arrow begins at 0 and ends at the fourth tick mark to the left of 0. Another arrow begins at the fourth tick mark to the left of 0 and ends at the first tick mark to the right of 0. An expression is . The difference is .