Liam has 9/10 gallon of paint for painting the bird houses he sells at the craft fair each birdhouse requires 1/20 gallon of paint how many birdhouses can liam paint

So to get the fractions easier to understand you need to put them on the same level you are on. So change the 9/10 gallons to 18/20 ( this makes them easier to deal with the 1/20)
so put 1/20 into 18/20. Liam can paint 18 bird houses.