To evaluate $a + 4$ when $a = 7$, substitute 7 for $a$ in the expression:

$a + 4 = 7 + 4 = 11$

Thus, the value of $a + 4$ when $a = 7$ is 11.

Would you like further details on this?

Here are 5 related questions to expand your understanding:

1. What would the expression $a + b$ equal if $a = 7$ and $b = 3$?
2. How would you evaluate $a - 5$ when $a = 7$?
3. Can you evaluate $2a + 4$ when $a = 7$?
4. What is the value of $a^2 + 4$ when $a = 7$?
5. How would you solve the equation $a + x = 11$ for $x$?

Tip: Always substitute values for variables carefully to avoid mistakes in algebraic expressions.