K = [tex]\frac{5}{9}[/tex](F - 32) + 273.15
To cancel out the 5/9, you can either multiply everything by the denominator and divide it down, or multiply everything by the reciprocal of the fraction ([tex]\frac{9}{5}[/tex]. Multiplying by the reciprocal is definitely easier if you can use a calculator:
[tex]\frac{9}{5}[/tex]K = (F - 32) + 491.67
Subtract 491.67 from both sides:
[tex]\frac{9}{5}[/tex]K - 491.67 = F - 32
Finish off by adding 32 to both sides:
[tex]\frac{9}{5}[/tex]K - 459.67 = F
Therefore, F = [tex]\frac{9}{5}[/tex]K - 459.67.
Hope this helps! :)