To solve this you must use a proportion like so...
65 is a percent and percents are always taken out of the 100. This means that one proportion will have 65 as the part and 100 as the whole
We want to know out of what number is 78 65%. This means 78 is the part and the unknown (let's make this x) is the whole
Now you must cross multiply
78*100 = 65*x
7800 = 65x
To isolate x divide 65 to both sides
7800/65 = 65x/65
120 = x
This means that 65% of 120 is 78
Hope this helped!
~Just a girl in love with Shawn Mendes