There are two wheat fields A and B with an average yield of 420 kg per mu. Block A wheat field has 5 mu, with an average yield of 450 kg per mu. If the average yield per mu of B wheat field is 400 kg, how many mu does B wheat field have?
有甲、乙两块麦田平均亩产420千克．甲块麦田有5亩，平均亩产450千克．如果乙块麦田平均亩产400千克，那么乙块麦田有多少亩．
<gadget id="calculator">450 * 5</gadget>
<output>2_250</output>

<gadget id="calculator">420 * 5</gadget>
<output>2_100</output>

<gadget id="calculator">2_250 - 2_100</gadget>
<output>150</output>

<gadget id="calculator">420 - 400</gadget>
<output>20</output>

<gadget id="calculator">150 / 20</gadget>
<output>15/2 = around 7.5</output>

<result>15/2 = around 7.5</result>