Teacher Wang spent 29 yuan and 70 cents to buy chalk, and 57 yuan and 90 cents to buy ink. She paid the salesperson 100 yuan, how much did she get back? (calculate with decimals)
王老师买粉笔用去29元7角，买墨水用去57元9角，她付给售货员100元，找回多少元？(用小数算)
<gadget id="calculator">7 / 10</gadget>
<output>7/10 = around 0.7</output>

<gadget id="calculator">29 + (7/10)</gadget>
<output>297/10 = around 29.7</output>

<gadget id="calculator">9 / 10</gadget>
<output>9/10 = around 0.9</output>

<gadget id="calculator">57 + (9/10)</gadget>
<output>579/10 = around 57.9</output>

<gadget id="calculator">(297/10) + (579/10)</gadget>
<output>438/5 = around 87.6</output>

<gadget id="calculator">100 - (438/5)</gadget>
<output>62/5 = around 12.4</output>

<result>62/5 = around 12.4</result>