Remember the rules for adding two numbers.
Adding two positive numbers gives a positive answer.
Adding two negative numbers gives a negative answer.
Examples
15 + 21 = 36
-15 + -21 = -36
Adding a negative number is the same as subtracting the positive.
The answer may be positive or negative depending on the size of the numbers.
Examples
25 + -31 = 25 - 31 = -6
25 + -3 = 25 - 3 = 22
Adding three positive and negative numbers is done in stages using the rules above.
Examples
25 + -31 + -1 = 25 - 31 - 1 = -6 - 1 = -7
25 + -3 + 5 = 25 - 3 + 5 = 22 + 5 = 27