stationery store has a total of 69 pens and brushes, each pen is 7.5 yuan, and each brush is 18 yuan. After all the brushes were sold, the writing brushes sold for 120 yuan more than the fountain pens. How many brushes are there? Solve the equation.
某文具店有钢笔和毛笔共69枝，钢笔每枝7.5元，毛笔每枝18元．全部卖出后，毛笔比钢笔多卖120元．毛笔有多少枝？用方程解．
<gadget id="calculator">69 * 7.5</gadget>
<output>517.5</output>

<gadget id="calculator">517.5 + 120</gadget>
<output>637.5</output>

<gadget id="calculator">18 + 7.5</gadget>
<output>25.5</output>

<gadget id="calculator">637.5 / 25.5</gadget>
<output>25</output>

<result>25</result>