Hi Jennifer,

There is an understood multiplication symbol between the 8 and the x in 8x. Likewise there is an understood multiplication symbol between (8x) and (-4). Thus you can think of (8x)(-4) as (8 times x) times (-4) or with symbols

(8 x) (-4)

Since multiplication is commutative (that is you can perform a string of multiplications in any order you want) you can write this as

(8) (-4) x = -32 x

Again using the convention of the understood multiplication

-32 x = -32x

Thus

(8x)(-4) = -32x

Now let me try the 4th problem, (6a)(3a)(-b²). Making the understood multiplication explicit this is

(6a)(3a)(-b²)

and using the commutative property of multiplication

(6a)(3a)(-b²) = 6 3 a a (-b²) = 18 a² b² = 18a²b²

Penny