Twice the number of A is 6.5 less than the number of B, and the number of B is 28. Find the number of A.
甲数的2倍比乙数少6.5，乙数是28，求甲数．
<gadget id="calculator">28 - 6.5</gadget>
<output>21.5</output>

<gadget id="calculator">21.5 / 2</gadget>
<output>10.75</output>

<result>10.75</result>