We are given the equation \( a = 3b \), where \( a \) is the number of shirts Wanda has, and \( b \) is the number of shirts Will has.
From the problem, we know that Wanda has 27 shirts, so we can substitute \( a \) with 27:
\[ 27 = 3b \]
To find \( b \), we need to solve for it:
- Divide both sides of the equation by 3:
\[ b = \frac{27}{3} \]
- Calculate \( \frac{27}{3} \):
\[ b = 9 \]
So, Will has 9 shirts.
The answer is B. 9.