There are two kinds of candies, A and B, whose unit price ratio is 4:5, and the weight ratio is 4:1. Mix the two kinds of candies together to form 100 kilograms of mixed sugar, and the unit price is 8.4 yuan. How much is the original unit price of A candy?
甲乙两种糖果，其单价比是4：5，重量比是4：1，把甲乙两种糖果混合在一起成为100千克的混合糖，单价为8.4元，甲糖果原来单价多少元？
<gadget id="calculator">8.4 * 100</gadget>
<output>840</output>

<gadget id="calculator">4 + 1</gadget>
<output>5</output>

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

<gadget id="calculator">100 * (4/5)</gadget>
<output>80</output>

<gadget id="calculator">4 * 80</gadget>
<output>320</output>

<gadget id="calculator">100 - 80</gadget>
<output>20</output>

<gadget id="calculator">5 * 20</gadget>
<output>100</output>

<gadget id="calculator">320 + 100</gadget>
<output>420</output>

<gadget id="calculator">840 / 420</gadget>
<output>2</output>

<gadget id="calculator">4 * 2</gadget>
<output>8</output>

<result>8</result>