not exactly sure what the exact code is for c++ however a lot if things derive from so it should be pretty similar to this:
float purchase = 95 ;
float stateTax = 6.5;
float countyTax = 2.0;
console.writeln (purcahse * (stateTax + countyTax));
//hope that helps. I used float so it produces the decimals. you could also use decimal though