Question 1129384
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The solution by tutor @josgarithmetic is not correct; he misread the given information about the weight of cast iron.<br>
The given information is that a plate of cast iron 1 foot square and 1 inch thick weighs 37.5 pounds.  Although it is unorthodox to do calculations in mixed units (square feet times inches), it is possible to do so if you pay attention to what you are doing.<br>
The volume of the given cylindrical disk is<br>
{{{(pi)(r^2)(h) = (22/7)(3.5^2)(4/3)}}} in units of square feet times inches.<br>
Then, since the given information about the weight of cast iron is in those same  mixed units, the weight of the disk is<br>
{{{(22/7)(3.5^2)(4/3)(37.5) = 1925}}}<br>