The answer is D I know that because I do this all the time
Since you have y alone on one side of the equation......
Use substitution and plug in 1/2x-4 for y in the other equation.

Distribute

Combine like terms

Add 8 to both sides

Divide by 4
and 
Plug this value in for x

Simplify

Multiply everything by 8 and simplify

Divide.....

Your answers are:

:
No.
Half of 48 would be 24, not 21
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Answer:
$24
Step-by-step explanation:
30X + 40
$24 IS THE RATE OF CHANGE