Subtract 7.5 from 5 times a number to get 3. Find this number. (solution by equation)
一个数的5倍减去7.5得3，求这个数．(用方程解)
<gadget id="calculator">3 + 7.5</gadget>
<output>10.5</output>

<gadget id="calculator">10.5 / 5</gadget>
<output>2.1</output>

<result>2.1</result>