To find the 7th value of the expression \( A^n = 2.5 + (n - 1)4 \), we can substitute \( n = 7 \) into the formula.
\[ A^7 = 2.5 + (7 - 1)4 \]
First, calculate \( 7 - 1 \):
\[ 7 - 1 = 6 \]
Now substitute this back into the equation:
\[ A^7 = 2.5 + 6 \times 4 \]
Next, calculate \( 6 \times 4 \):
\[ 6 \times 4 = 24 \]
Now, substitute \( 24 \) into the equation:
\[ A^7 = 2.5 + 24 \]
Finally, add \( 2.5 \) and \( 24 \):
\[ A^7 = 26.5 \]
Thus, the 7th value of \( A^n \) is
\[ \boxed{26.5} \]