Question 1153621
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One way...
Compute area in square feet:
{{{ 9ft x 21ft = 189ft^2 }}}
Convert square feet to square yards:
{{{189ft^2 * (1yd^2/9ft^2) = 21yd^2}}}
Multiply square yards by price per square yard
{{{matrix(1,7, 21, "yd^2 ", " *", " $", 26.50, "/yd^2", "= $556.50") }}}

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I carried along the units to illustrate how they can help keep things straight.  For example, in the conversion to square yards, notice how {{{ft^2}}} will cancel, leaving {{{ yd^2}}}