The number of roses planted by the students is 25% of that of sunflowers, and the number of roses planted is 21 less than that of sunflowers. How many roses are planted?
同学们种月季花的棵数是向日葵的25%，种的月季花的棵数比向日葵少21棵，种月季花多少棵？
<gadget id="calculator">25 / 100</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">1 - (1/4)</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">21 / (3/4)</gadget>
<output>28</output>

<gadget id="calculator">28 - 21</gadget>
<output>7</output>

<result>7</result>