Question 1202500
<pre>
     PRICES         QUANTITY       COST
       7              30-d        7(30-d)
       9               d           9d
TOTAL                 30            250
<pre>
d, how many deluxe pizzas


{{{highlight_green(7(30-d)+9d=250)}}}


{{{7*30-7d+9d=250}}}

{{{(9-7)d=250-7*30}}}

{{{d=(250-7*30)/(9-7)}}}

{{{d=20}}}

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