food store bought a batch of biscuits at 10.5 yuan per kilogram, and sold them at 11.4 yuan. When the biscuits were sold until there were 5 kilograms left, they not only recovered the total cost but also made a profit of 51 yuan. How many kilograms of this kind of biscuits did they buy? ?
某食品店以每千克10.5元购进一批饼干，售价为11.4元，这种饼干卖到还剩5千克时，不仅收回了总成本还获利51元，问这种饼干购进多少千克？
<gadget id="calculator">11.4 * 5</gadget>
<output>57</output>

<gadget id="calculator">57 + 51</gadget>
<output>108</output>

<gadget id="calculator">11.4 - 10.5</gadget>
<output>0.9</output>

<gadget id="calculator">108 / 0.9</gadget>
<output>120</output>

<result>120</result>