84.6÷75. You can estimate that the answer is going to be just over 1 because 84 is only a bit bigger than 75. This tells you the answer is going to be 1 point something. Now you know where the decimal point is.
You can use long division 75 ) 84600... And that will give you 11280..., ignoring the decimal point. But you know the answer is a little bigger than 1, so put in the decimal point 1.128 (we don't need any more zeroes).
There's an easier way: 84.6÷75 can be written 846/75 as a fraction which cancels down a bit by dividing top and bottom by 3: 282/25. So we now have to divide 282 by 25. But 25=5*5 so we can divide by 5 twice: 282/5=564 (ignore the decimal point and treat this as 2820/5). Now divide again by 5: 564/5=1128 (ignore the decimal point). So we have the figures for the final answer, and all we have to do is to put the decimal point in: 1.128 because we know that the answer is only a little bigger than 1.
There's a trick you can use when dividing by 25. You multiply by 4 instead (because 25=100/4 or 1/25=4/100 multiply by 4 and divide by 100): 4*282=1128. As we had before. Again, we just add the point: 1.128.