The problem asks to simplify the given expression $(-8 + 7i) - (3 - 6i)$ into the standard form $a + bi$.

Step 1: Expand the terms

$(-8 + 7i) - (3 - 6i) = -8 + 7i - 3 + 6i$

Step 2: Combine like terms

Combine the real parts: $-8 - 3 = -11$

Combine the imaginary parts: $7i + 6i = 13i$

Final Answer:

$-11 + 13i$

The expression in standard form $a + bi$ is: $\boxed{-11 + 13i}$

Would you like further clarification or examples? Here are some related questions to deepen your understanding:

1. What is the geometric interpretation of complex numbers in the form $a + bi$?
2. How do you add or subtract complex numbers graphically?
3. What are the differences between standard form and polar form of complex numbers?
4. Can you multiply and divide complex numbers? How do their forms change?
5. What is the conjugate of a complex number, and how is it used in simplifications?

Tip: Always group real and imaginary terms separately when simplifying expressions involving complex numbers!