Idon't understand can someone me 6 ( x - 8 ) = -84 

First, open the brackets (rule No 1)

By multiplying what is outside the bracket by what is inside the bracket

( 6 × X ) + ( 6 × -8 ) = -84

This will give you

6x + -48 = -84

Always a + and a - will give you a -

6x - 48 = -84

Collect like terms by moving the -48 to the other side. This becomes +48

(Always when a number changes side, it also changes sign)

6x = -84 +48

6x = -36

Divide by 6 to stay with X only.

(When you have a product you have to divide to take what you don't want)

X = -36 ÷ 6

X = -6 (minus sign remains)

(Minus sign gets out only when you are dividing a -number by another -number)
They cancel each other

The answer would be: b