Percent just means "out of 100", so 50% is , 38% is , etc.
On the second problem, you multiply something by to get 5.7. Since division is the opposite of multiplication, the "something" you want is the product, 5.7, divided by or 5.7 divided by .
To multiply and divide the fractions, first change the whole number + fraction to just a fraction - like . Then you can multiply and divide by only whole numbers. Remember that dividing by a fraction is the same as inverting the fraction and multiplying.
The third one is just the "out of 100" rule - is just . Now you just need to change it to a normal fraction - whole number divided by whole number.
Post again in this thread if you're still having trouble. By the way, where are you studying math?