Simplify the expression to a + bi form:

To simplify the expression \((-4 + 10i) + (5 + 3i)\), you can combine the real parts and the imaginary parts separately.

1. Combine the real parts: \[ -4 + 5 = 1 \]

2. Combine the imaginary parts: \[ 10i + 3i = 13i \]

Now, putting it all together, we get: \[ 1 + 13i \]

Thus, the expression simplifies to: \[ \boxed{1 + 13i} \]