hmm is very straight forward, how much is whatever% of anything? is just (whatever/100) * anything.
[tex]\bf \textit{4\% of 2,500}\implies \cfrac{4}{100}\cdot 2,500\implies 100
\\\\\\
\textit{the rest is 7,500 at 5\%, what's 5\% of that?}\implies \cfrac{5}{100}\cdot 7,500\implies 375[/tex]
