Start by simplifying the fractions, its usually easier to leave it as a top heavy fraction. So we would do 420/180 which can be simplified to 7/3 (we can divide both the top and botton of the fraction by 60) Then we can do 54/180 which is 3/10. Now we have some nicer fractions all we have to do is multiply 7/3 x 3/10. To do this we can just multiply the tops and bottoms of the fractions so we get 21/30. This can be simplified one last time to get a final answer of 7/10 or 0.7