pretty simple setup. set a global variable for score and increment it for each whack. When game is over set hiscore variable to score variable if score variable is larger.
if Score > HiScore then HiScore = Score
of course for permanent save, output to an .ini file is simplest
open "Whakamole.ini" for output as #1
print #1, HiScore
close #1

use Input #1 to read it again.