You currently have:
-2.3 -(4.5 -3.5)
To solve for this, we need to use PEMDAS (Parenthesis, Exponents, Multiply, Divide, Add, Subtract).
We have parenthesis, so work what's in parenthesis first.
4.5 - 3.5 = 1.0
You are left with:
-2.3 -1.0
When subtracting from a negative, you basically adding two positive numbers, just the sum will be negative instead of positive.
-2.3 -1.0 = -3.3
Your final answer is -3.3
I hope this helps!