To find out how many servings Frank can make with 85 tablespoons when each serving is 2 1/2 tablespoons, you can divide the total amount of tablespoons by the amount per serving.
First, convert 2 1/2 tablespoons to an improper fraction:
\[ 2 \frac{1}{2} = \frac{5}{2} \]
Now, divide 85 by \(\frac{5}{2}\):
\[ 85 \div \frac{5}{2} = 85 \times \frac{2}{5} = \frac{85 \times 2}{5} = \frac{170}{5} = 34 \]
Therefore, Frank can make 34 servings with 85 tablespoons of salad dressing.