Let \( x \) be the price of each shrub.
The customer spent $17.50 on potting soil and bought 4 shrubs, which means the total cost for the shrubs is \( 4x \).
The total bill is the sum of the cost of potting soil and the cost of shrubs, which can be represented by the equation:
\[ 17.50 + 4x = 53.50 \]
Now, we'll solve for \( x \):
- Subtract $17.50 from both sides of the equation:
\[ 4x = 53.50 - 17.50 \]
\[ 4x = 36.00 \]
- Divide both sides by 4 to solve for \( x \):
\[ x = \frac{36.00}{4} \]
\[ x = 9.00 \]
Thus, the price of each shrub is \( \boxed{9.00} \).