Answer
a) $f^{-1}=(F-32)/1.8$.
b) $30$ Celsius degrees.
Work Step by Step
a) If we want to get a formula for the inverse function, we swap $x$ and $y$ and solve for $y$.
Hence, after swapping $x$ and $y$, we get:
$x=1.8y+32\\x-32=1.8y\\y=f^{-1}=(F-32)/1.8$.
This represents the Celsius degrees associated with the Fahrenheit degrees $F$.
b) Plugging in $86$ into the inverse formula above, we get: $30$. Thus, $86$ degrees Fahrenheit is the same as $30$ Celsius degrees.
