Question

Simplify the expression: z2-z (z+3)+3z

Answer 1

We have z2-z(z+3)+3z. We have to remember order of operation. First operation inside the parenthesis, then multiply/divide and finaly add/subtract.
Lets do this
$z^2-z(z-3)+3z$
First we have to multiply -z by each argument inside the parenthesis.
$z^2-z^2+3z+3z=6z$ 
Finally we can simplify z^2 with -z^2 and 3z with 3z to get the result 6z.