You set your equation up like this. part/whole = percent/100. Since you are trying to find the part you set your equation up like this x/150 = 40/100. Now, you cross multiply you have x*100 = 150*40 then you multiply and get 100x = 6,000 now you have to find what x equals so you do 100x/100 = 6,000/100 and you get x= 60. So, $60 is 40% of $150.