Aunt Li wanted to buy some hydrating masks. She went to the cosmetics store and found that the original price of 7.5 yuan per hydrating mask is now holding a "buy 8 get 1 free" event. She bought 18 pieces in total. How much is the minimum cost? ?
李阿姨想购买一些补水面膜，到化妆品商店一看，原价每片7.5元的补水面膜，现在正举办"买八送一"的活动，她连买带送共购了18片，至少需多少元？
<gadget id="calculator">8 / 9</gadget>
<output>8/9 = around 0.888889</output>

<gadget id="calculator">7.5 * (8/9) * 18</gadget>
<output>120</output>

<result>120</result>