in english explain what this code segment does.

EASY$=0$

NORMAL$=1$

HARD$=2$

grade$=80$

def adjustGrade$($oldGrade$,$ bonus, difficulty$)$:

if difficulty$==$EASY:

newGrade$=$oldGrade $($bonus$*0\mathrm{.}5)$

elif difficulty$==$NORMAL:

newGrade$=$oldGrade$+$bonus

elif difficulty$==$HARD:

newGrade$=$oldGrade$+($bonus$*2)$

return newGrade

grade$=$adjustGrade$($grade$,20,$ EASY$)$