Percent is [tex] \frac{percent}{100} [/tex]. and if the kicker makes [tex] \frac{4}{5} [/tex], just compare the two like this:
[tex] \frac{4}{5} = \frac{x}{100} \\
4*100=5*x\\
x=\frac{400}{5}=80[/tex]
So the percent of extra kicks the kicker made is 80%.