Step 1:

“... the distance between Exits 77 and 79 on Interstate 29 is 2 miles. On the map, this distance is $\frac{3}{4}$of an inch.” This information translates to:

“2 miles in the real worlds is equivalent to $\frac{3}{4}$ inch on the map”

Step 2:

And we are asked to find the distance in the real world that is equivalent to $3\frac{3}{8}$ inches on the map:

$$\frac{x}{3\frac{3}{8}}=\frac{2}{\frac{3}{4}}$$

$$\therefore x=\frac{2}{\frac{3}{4}}\times 3\frac{3}{8}=9$$