Good advice would be to use the calculator that comes on all computers up to date. You could also do it by aligning the decimal points while solving the problem as you would any other problem with double digits or more. And, when you add a negative to a negative, it creates a larger negative number. When you add a positive number to a negative number, it is the same as subtracting. For extra special ones, such as 3, when you subtract a negative number from another negative number, you would take the negative number on the right, and change it to a positive to a positive, because two negatives create a positive. So, #3 would be -3.48 + 3.5, which would be .02.
