Answer:
Option B
Step-by-step explanation:
As here,
In all the options processes in 3rd step .
<u>As</u><u> </u><u>the</u><u> </u><u>bases</u><u> </u><u>are</u><u> </u><u>same</u><u> </u><u>exponents</u><u> </u><u>get</u><u> </u><u>added</u><u>. </u>
And in Option B 3rd step it has been correctly done form of,

Is correct simplification.
The constant of proportionality represents the unit cost .You use the equation y = 8.5 x to calculate the total cost y in dollars for x in what ever you are buying