20.
a)...=6×9=54
b)...=2×3×4×5=120
c)...=2+3+4=9
d)...=|12| = 12
e)...=radical din 50625 = radical din 225 = 15
d)...=|-5|=5
e)...=|-5|×|-3|=5×3=15
f)...=1