Perform the operation

-3 + (-10)

-3 + (-10) = -3 - 10 = -13

To perform the operation -3 + (-10), you simply add the two numbers together:

-3 + (-10) = -3 - 10

Now, to simplify this expression, you add the numbers:

-3 - 10 = -13

Therefore, -3 + (-10) equals -13.