If the 300 inspected light bulbs represent 20% of an hour's total production of light bulbs, how many light bulbs are produced in an hour

You can write this algebraically. 20% of a number is that number multiplied by 0.2, so 300 = 0.2x

Dividing by 0.2 (i.e. multiplying by 5) gives us x being 1500.
So 1500 light bulbs are produced in an hour.