What do we do if there's more than two numbers?

There's a pretty easy way to do it, but let's do a couple with the car first so we can see what's going on:

-5 + 3 + 7 + -1 + -4 =

press the purple "play" button to start the car

-5 + 3 + 7 + -1 + -4 = 0

Look what happens if we group all the positives...

3 + 7 = 10

and all the negatives...

-5 + -1 + -4 = -10

and add those answers together:

10 + -10 = 0

Yep, that's the answer we got with the car!