The two fractions have the same denominator.
They both have the same denominator, so you can combine them:
z and -5z have the same variable so you could look at it like this: z -z -z -z -z -z
it should be clear then that they combine to equal -4z
both terms in the numerator are multiples of -2, so factor out a -2
And since -2 is multiplied and divided by 2z+3, the 2z+3 cancels out to equal one
Anything times 1 is itself
distribute the minus sign
combine like terms
There are other ways to simplify from here, but "simplify" is kind of ambiguous, this answer is probably what her book is looking for.
Anyway, with that negative sign, it applies to the whole term. You could think of it like this also:
Or it may help to work backwards:
However you want to look at it, just understand the sign out front needs to get distributed.
so z+19z = z(1+19) = 20z
3z and 19 are not like terms. So and z are not like terms.
You would do it like this:
Split up the numerator
group them (you don't have to do all these steps I'm doing, but I want to hit every step along the way to make it easier to see)
Factor out a 3z
Factor out a 5
Factor out a (z+5)
z+5 is in the numerator and the denominator, so it cancels out
In simple arithmetic, you combine fractions without a common denominator by first finding the least common multiple of both denominators, and then multiplying the numerator and denominator of both fractions by the necessary amount to change the denominator to that multiple. For example:
The least common multiple of 2 and 3 is 6, so we do
This basic process doesn't change with the introduction of variable expressions. We have:
The least common multiple of and is , so we simplify thus:
You should be able to take it from here.