In order to encourage saving electricity, the power company stipulates that the electricity fee shall be calculated according to the following method. The monthly electricity consumption shall not exceed 100 kwh, and the charge shall be 0.55 yuan per kwh. The charge is 0.75 yuan per kilowatt-hour. Xiaohong’s family paid 85 yuan for electricity last month. How many kilowatt-hours did his family use last month?
为了鼓励节约用电，电力公司规定按以下方法计算电费，每月用电不超过100千瓦时，按每千瓦时0.55元收费，每月用电超过100千瓦时，超过100千瓦时的部分按每千瓦时0.75元收费，小红家上个月付85元电费，他家上个月用电多少千瓦时？
<gadget id="calculator">0.55 * 100</gadget>
<output>55</output>

<gadget id="calculator">85 - 55</gadget>
<output>30</output>

<gadget id="calculator">30 / 0.75</gadget>
<output>40</output>

<gadget id="calculator">40 + 100</gadget>
<output>140</output>

<result>140</result>