Answer in explanation:
although there's an addition sign, you subtract the two because a
(+) + (-) = (-) subtract
[This is a general rule, writing down the "rules" for reference is a good way to help if your having trouble]
subtract to find your answer (you keep the sign of 1.8 because it's the larger number.)
1.3 + (-1.8) =
-0.5
-0.5 is your answer
Hope this is clear!