□, △ and ○ are all tens, and □*△=4200, △*○=3000, then ○*□=how many.
□、△和○都是整十数，并且□*△=4200，△*○=3000，那么○*□=多少．
<gadget id="calculator">4_200 / 60</gadget>
<output>70</output>

<gadget id="calculator">3_000 / 60</gadget>
<output>50</output>

<gadget id="calculator">70 * 50</gadget>
<output>3_500</output>

<result>3_500</result>