I don't understand what it means when they say write an expression with a variable. could you please write an example for me? Thank you.

Common textbook problems ask students to write an
algebraic expression to resemble a verbal expression.  For instance, "eight less than a
number" translates to n-8. Algebraic expressions are a concise way to write lengthy
verbal expressions.  The following are a few more
examples.

The sum of seven times a number and
3.

7x + 3

The product of two
and the sum of a number and 9.

2(x +
9)

Twelve more than the quotient of a number and
nine.

x/9 + 12

The quotient of
a number and the sum of twelve and nine.

x/(12 +
9)

When writing an algebraic expression, make sure to read
the verbal statement carefully.  Most mistakes are caused by trying to get the problems
done quickly.