Unexpected token else

I have been doing javascript on codecademy the last few months. I decided to try to write my own script. Here it is:

var miles = prompt("How many miles did you travel?")
if (miles <= 10){alert (miles * 0.10)};
else if (miles > 10){alert (((miles - 10) * 0.25)+1)};
else(miles > 20){alert (((miles - 20) * 0.50)+3.50)};

The javascript console is returning "Unexpected token else" and I can't figure out whats wrong. Anyone have any suggestions?