A.
1min = \frac{1}{60}h
5min = \frac{5}{60}h = \frac{1}{12}h
20min = \frac{20}{60}h = \frac{1}{3}h
30min = \frac{30}{60}h = \frac{1}{2}h
h - inaczej godzina, używane w obliczeniach, żeby nie pisać długo godzina
B.
1mm = \frac{1}{10}cm
5mm = \frac{5}{10}cm = \frac{1}{2}cm
9mm = \frac{9}{10}cm