The number A is 21 more than the number B. The ratio of A and B is 4:1. What is the number A?
甲数比乙数多21，甲、乙两数的比是4：1，甲数是多少
<gadget id="calculator">4 - 1</gadget>
<output>3</output>

<gadget id="calculator">21 / 3</gadget>
<output>7</output>

<gadget id="calculator">7 * 4</gadget>
<output>28</output>

<result>28</result>