diff --git a/education/software development/ECE1400/Chapter 15 Exercises.md b/education/software development/ECE1400/Chapter 15 Exercises.md
index 3675fc5..ef5a070 100644
--- a/education/software development/ECE1400/Chapter 15 Exercises.md	
+++ b/education/software development/ECE1400/Chapter 15 Exercises.md	
@@ -18,6 +18,7 @@ Yes, `""` is a path relative to the current file, whereas `<>` is a path to the
 
 > **4.** Assume that `debug.h` is a header file with the following contents...
 >(a). What is the output when the program is executed?
+
 ```
 Output if DEBUG is defined:
 Value of i: 1
@@ -25,5 +26,13 @@ Value of j: 2
 Value of i + j: 3
 Value of 2 * i + j - k: 1
 ```
+
 > (b). What is the output if the `#define` directive is removed from `testdebug.c`?
-> 
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+
+```
+Output if DEBUG is not defined:
+```
+
+> (c). Explain why the output is different in parts (a) and (b)
+
+When `DEBUG` is defined, any instances of the `PRINT_DEBUG` token are replaced with a `printf` call during compile time, but when it's not defined, they're replaced with nothing.
\ No newline at end of file