The expression for "a number plus 3, multiplied by 6" is:

$6 \times (x + 3)$

where $x$ represents the unknown number.

Let me know if you need further clarification or if you'd like additional details on how this expression works!

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Here are some related questions:

1. How can you simplify the expression $6 \times (x + 3)$?
2. What happens if we change the order of operations in the expression?
3. How would the expression change if it said "the number minus 3" instead of plus 3?
4. How would you solve for $x$ if you were given the equation $6 \times (x + 3) = 42$?
5. What is the distributive property, and how does it apply to this expression?

Tip: Always remember the order of operations (PEMDAS/BODMAS) when dealing with expressions.