Xiaoqiao and her mother went to the flower shop to buy flowers. Her mother bought some roses for 2.5 yuan each for 100 yuan, and bought a vase for 28 yuan. When she got back 42 yuan, how many roses did her mother buy? (column equation)
小巧和妈妈一起去花店买花，妈妈用100元买了一些2.5元一支的玫瑰，又买了一个28元的花瓶，找回42元，妈妈买了多少支玫瑰？(列方程)
<gadget id="calculator">100 - 28 - 42</gadget>
<output>30</output>

<gadget id="calculator">30 / 2.5</gadget>
<output>12</output>

<result>12</result>