The forest farm plans to plant a batch of trees. On the first day, 30% of the trees were planted, and on the second day, 50% of the trees were planted. It is known that 45 trees were planted on the second day. How many trees did you plant on the first day?
林场准备栽一批树，第一天栽了这批树的30%，第二天栽了这批树的50%，已知第二天栽树45棵．第一天栽树多少棵？
<gadget id="calculator">50 / 100</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">45 / (1/2)</gadget>
<output>90</output>

<gadget id="calculator">30 / 100</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">90 * (3/10)</gadget>
<output>27</output>

<result>27</result>