Question 1153891
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<pre>

One-equation setup is THIS equation


    3.94x + 1.89*(7-x) = 21.43.


From the equation, express x and calculate


    x = {{{(21.43-7*1.89)/(3.94-1.89)}}} = 4.


<U>ANSWER</U>.  4 for $3.94 and (7-4) = 3 for $1.89.
</pre>

Solved.


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Ignore post by @josgarithmetic, &nbsp;since it is &nbsp;&nbsp;<U>W R O N G</U>&nbsp;&nbsp;  (as usual).