100 cm = 1 meter or 1 cm = 0.01 m. So 1.50 cm = 0.0150 m. A meter is larger so there are less of them.
1000 g = 1 Kg or 1 g = 0.001 Kg. So 30 g = 0.03 Kg.
A Joule is a unit of energy and horsepower is a unit of power. ! Joule per second = 1 Watt and 746 Watt = 1 hp so 1 hp = 746 J/s. Therefore if you divide a Joule by hp you'll get seconds. When dividing by J/s you invert and multiply so it looks like (s/J)(J) and thus Joules cancels out. J Joule divided by 1 hp is (1/746) of a second.