Solve the equation: 18+15x=21.
解方程：18+15x=21．
<gadget id="calculator">21 - 18</gadget>
<output>3</output>

<gadget id="calculator">3 / 15</gadget>
<output>1/5 = around 0.2</output>

<result>1/5 = around 0.2</result>