Question

What is -13.5+40.5 plz tell me

Answer 1

To add a negative number to a positive number, you need to subtract.  So take 40.5 and subtract 13.5. That will give you 27.

Answer 2

-13.5+40.5
Is the same as
40.5-13.5
Solve
40.5-13.5= 27