Answer
one-to-one
Work Step by Step
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$y=f(x)=4x+20$
Assume that $f(a)=f(b)$
$\ \ \Rightarrow \ \ 4a+20=4b+20\qquad /-20$
$\ \ \Rightarrow \ \ 4a=4b\qquad /\div 4$
$\ \ \Rightarrow \ \ a=b$
$f$ is one-to-one
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