To find the midpoint \( M \) of two points \( A \) and \( B \), you can use the formula:
\[ M = \frac{A + B}{2} \]
Given that \( A = 20 \) and \( B = 54 \):
\[ M = \frac{20 + 54}{2} = \frac{74}{2} = 37 \]
Therefore, the midpoint \( M \) of \( A \) and \( B \) is \( 37 \).