The key phrase is "...more than..." This indicates that we should add two things.
... + ...The two terms that we are adding together are: "six" and "a number." There are two ways in which we can write it.
6+a number or a number + 6
Let's choose the first option. When we say "a number," this is indicating an arbitrary number or a variable. If we call this number x, we can complete our expression.
six more than a number
6 + x
Note that this is only one of multiple ways to algebraically express the given verbal expression.
