Xiaomei and Xiaoying folded some little red flowers together. If Xiaomei folds 7 days first, and then Xiaoying folds 6 days, then 25% of these small red flowers are folded. It is known that Xiaoying's flower folding efficiency is higher than Xiaomei's (1/3). Then, how many days would it take for Xiaomei to fold these little red flowers by herself?
小美、小颖一起折一些小红花．如果先由小美折7天，再由小颖折6天，则折完这些小红花的25%，已知小颖的折花效率比小美高(1/3)．那么，这些小红花若由小美单独折完需要多少天．
<gadget id="calculator">25 / 100</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">6 * (1/3)</gadget>
<output>2</output>

<gadget id="calculator">7 + 6 + 2</gadget>
<output>15</output>

<gadget id="calculator">(1/4) / 15</gadget>
<output>1/60 = around 0.016667</output>

<gadget id="calculator">1 / (1/60)</gadget>
<output>60</output>

<result>60</result>