It is known that an alloy weighing 63 grams contains copper and zinc. Now add 7 grams of copper. The ratio of copper to zinc in the new alloy is 3:2. If the ratio of copper to zinc in the original alloy is 1:a, find a.
已知一块重63克的合金含有铜和锌，现在加入铜7克，新合金铜和锌的比是3：2，若原来的合金中，铜与锌之比是1：a，求a．
<gadget id="calculator">3 + 2</gadget>
<output>5</output>

<gadget id="calculator">4 / 5</gadget>
<output>4/5 = around 0.8</output>

<result>4/5 = around 0.8</result>