The fruit shop ships 30 boxes of watermelons, priced at 50 yuan each; 40 boxes of apples, priced at 20 yuan each. A total of 1,800 yuan was sold in one day. What is the minimum number of boxes of watermelons and apples sold in total?
水果店运来西瓜30箱，每箱售价50元；苹果40箱，每箱售价20元．一天一共卖得1800元．一共卖出的西瓜和苹果最少多少箱？
<gadget id="calculator">30 * 50</gadget>
<output>1_500</output>

<gadget id="calculator">1_800 - 1_500</gadget>
<output>300</output>

<gadget id="calculator">300 / 20</gadget>
<output>15</output>

<gadget id="calculator">30 + 15</gadget>
<output>45</output>

<result>45</result>