Find the missing value for the multiplication equation 9/10 = x 10

Simple (Cross multiplication ) 

9        x
_        _                      = 90/10 = 9

10      10 

-20

Step-by-step explanation:

My math teacher taught me a trick when working with negative numbers: Same, Change, Change.

Basically, the first number is kept the same, the operation (in this case, the plus sign) is changed to its opposite, and the third number is changed to its inverse.

So, in this case:

-4+(-16)

-4-16

The plus sign was changed to a subtraction sign and -16 was changed to 16.

This trick works with problems like these. It's helped me a lot.

-4-16= -20

If you're still confused, I've always liked to think of it as 4+16=20. Then just put  a negative sign in the front. So, -20.

Hope this helped!