You can't, really. It is only for **natural number multipliers** that you can equate multiplication with **repeated addition**.

But you can come close.

Multiplying -3 by **3** can be thought of as **starting with 0** and doing 3 additions of -3: 0 + -3 + -3 + -3 = -9. Multiplying -3 by **-3** can be thought of as **un**doing 3 additions of -3: 0 **-** -3 **-** -3 **-** -3 = 9, just as subtraction can be thought of as undoing an addition, and adding a negative number as undoing an addition of a positive number.