ANSWER
25%
EXPLANATION
The percent difference is:
[tex]\frac{\text{ final score - initial score}}{\text{ initial score}}\times100[/tex]In this problem, the initial score was 72 and the final score was 90:
[tex]\frac{90-72}{72}\times100=\frac{18}{72}\times100=0.25\times100=25\text{ \%}[/tex]