The expression "a number" can be represented with any letter. Use, for instance, the letter n.
Then, the expression "The quotient of a number and 6" can be represented as:

9 more than the quotient of a number and 6 can be expressed as:

If that expression is equal to 3, then:

Which is an algebraic expression for "9 more than the quotient of a number and 6 is 3".