Hello there!
So basically all you have to do is remove these signs that makes it complicated. However, you must know the rules in order to do so.
The rules says:
When you have plus sign * negative sign, the answer will carry the negative sign.
So let's start!
20 + (-3.05) + (-9.5)
= 20 - 3.05 - 9.5
= 16.95 - 9.5
= 7.45
I hope this helps and please let me know if you have questions about the answer.
Good luck with your studies!
Happy New Year!