12 is multiplied by some number, that product is reduced by 9, and the total is equal to 37

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12 is multiplied by some number, that product is reduced by 9, and the total is equal to 37

The phrase some number means an arbitrary variable, let's call it x.

12 multiplied by this number:
12x

The product of 12x is reduced by 9
12x - 9

The phrase the total is equal to means an equation, so we set 12x - 9 equal to 37:
12x - 9 = 37