Hi Erin, Three important rules to remember here.

1)When ever you have 2 signs right next to each other get it down to 1. When the 2 signs are different make it - and when they are both the same make it +.

Once you have eliminated 2 signs right next to each other then combine the numbers.

2)If the two numbers have the same sign in front of them just add the two numbers and retain the sign they both have. A number without a sign in front of it implies +.

3)If the two numbers have a different sign in front of them take the difference between the 2 numbers and give it the sign of the bigger number.

For your example -4+-3 becomes -4-3 using rule 1. The answer is -7 using rule 2.

For your example -2+7 the answer is 5 using rule 3. The + in front of the 5 is implied.

Hope this helps.