SOLUTION: f(x)=5x-4 f(4a)=80 what is a equal to?

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Question 911454: f(x)=5x-4
f(4a)=80
what is a equal to?
Answer by MathLover1(20849) About Me  (Show Source):
You can put this solution on YOUR website!

f%28x%29=5x-4+
f%284a%29=80 => means x=4a
80=5%2A4a-4+ ...solve for a

80=20a-4+
80%2B4=20a+
84=20a+
84%2F20=a+
4.2=a+
check:
f%284a%29=80
f%284%2A4.2%29=80
f%2816.8%29=80 check that f%2816.8%29=5x-4+ =>f%2816.8%29=5%2A16.8-4+ =>f%2816.8%29=84-4+ =>f%2816.8%29=80+