It is known that ab=c, if a increases by 30 and c remains unchanged, how much will b increase
已知a-b=c，如果a增加30，c不变，那么b将要增加多少
<gadget id="calculator">100 - 60</gadget>
<output>40</output>

<gadget id="calculator">130 - 40</gadget>
<output>90</output>

<gadget id="calculator">90 - 60</gadget>
<output>30</output>

<result>30</result>