1. which is an example of an algebraic expression?
4(3 + 8)
182
3 – a
21 • 4
2. which is an algebraic expression for 5 more than z?
5z
z + 5
5z + 5
5 – z
3. which word phrase can be used to represent the algebraic expression 4(21 + n)?
4 plus the sum of 21 and a number n
4 times the product of 21 and a number n
4 times the sum of 21 and a number n
4 less than the sum of 21 and a number n

The answers are --> 

1.) 3 -a. An algebraic expression needs have a variable in it. In this case the variable is "a". So the answer is --> 3-a

2.) z+5. 5 more that z means 5 added to z. So, the answer is --> z+5

3.) 4 times the sum of 21 and a number n. In an algebraic expression, the brackets takes the highest order of preference. So, the answer is --> 4 times the sum of 21 and a number n