1. **State the problem:** Calculate the value of $-45 - (-30)$. 2. **Recall the rule:** Subtracting a negative number is the same as adding its positive counterpart. So, $a - (-b) = a + b$. 3. **Apply the rule:** Replace $-(-30)$ with $+30$, so the expression becomes $-45 + 30$. 4. **Perform the addition:** $-45 + 30 = -15$. 5. **Final answer:** The value of $-45 - (-30)$ is $-15$.