When Xiao Ming calculated a subtraction formula, he mistook the subtrahend 24 as 42, and the result was 51. What is the correct number?
小明在计算一道减法算式时，误把减数24看成了42，结果得51，正确的得数是多少？
<gadget id="calculator">42 - 24</gadget>
<output>18</output>

<gadget id="calculator">51 + 18</gadget>
<output>69</output>

<result>69</result>