When you are dividing by a decimal, you have to move the decimal to the right however many places to make it a whole number. In this case if you move the decimal 1 place to the right (that means multiplying by 10) .8 becomes 8. However many places you move the decimal, you have to do the same for the other number. In this case 30.0 becomes 300. Now the problem becomes 300 ÷ 8.
Simple, by the way, it's 30 divided by 0.8, no wonder why you got weird numbers I guess. Move the decimal places back 1 time, you should get 300 divided by 8. Then just divide, the answer is 37.5
