Xiao Ming went to the store to buy 66 red and black pens in total. Each red pen is priced at 5 yuan, and each black pen is priced at 9 yuan. Because the quantity bought is large, the store will give a discount. The red pen pays 85% of the price, and the black pen pays 80% of the price. If he pays 18% less than the price. So how much did he buy the red pen?
小明到商店买红、黑两种笔共66支．红笔每支定价5元，黑笔每支定价9元．由于买的数量较多，商店就给予优惠，红笔按定价85%付钱，黑笔按定价80%付钱，如果他付的钱比按定价少付了18%．那么他买了红笔多少．
<gadget id="calculator">9 * 66</gadget>
<output>594</output>

<gadget id="calculator">18 / 100</gadget>
<output>9/50 = around 0.18</output>

<gadget id="calculator">9 * 66 * (9/50)</gadget>
<output>2_673/25 = around 106.92</output>

<gadget id="calculator">80 / 100</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">9 * (4/5) * 66</gadget>
<output>2_376/5 = around 475.2</output>

<gadget id="calculator">594 - (2_673/25) - (2_376/5)</gadget>
<output>297/25 = around 11.88</output>

<gadget id="calculator">5 * (9/50)</gadget>
<output>9/10 = around 0.9</output>

<gadget id="calculator">85 / 100</gadget>
<output>17/20 = around 0.85</output>

<gadget id="calculator">5 * (17/20)</gadget>
<output>17/4 = around 4.25</output>

<gadget id="calculator">9 * (9/50)</gadget>
<output>81/50 = around 1.62</output>

<gadget id="calculator">9 * (4/5)</gadget>
<output>36/5 = around 7.2</output>

<gadget id="calculator">(17/4) - 5 - (81/50) - (36/5)</gadget>
<output>-957/100 = around -9.57</output>

<gadget id="calculator">(9/10) + 9 + (-957/100)</gadget>
<output>33/100 = around 0.33</output>

<gadget id="calculator">(297/25) / (33/100)</gadget>
<output>36</output>

<result>36</result>