Think of letters (like x or y) as 'magic boxes' containing unknown numbers. They are useful tools for creating rules that work no matter what number you put inside.
Write a × 3 as 3a. The rule is to put the number first.
Write 1 × x simply as x, not 1x.
2x + 3x can be combined into 5x. You can add boxes of the same kind together.
Formula
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