in order to calculate a percentage all you need to do is times the number that you want to know the percentage of by the percentage needed and then divide by 100...

so for 65% of 160 you would...

first times it by 65... = 10400

then divide by 100... = 104

thus 65% of 160 is 104... this is because a percentage is really a short hand of the number divided by 100... (for 65 this is 65/100)... and whenever there is an 'of' in a maths question it usually means times and so it's the number times the percentage(which is a fraction)

hope that helps!!