Chapter 6 Rational Exponents and Radical Functions - 6.3 Perform Function Operations and Composition - 6.3 Exercises - Problem Solving - Page 433: 45b

$61.5$

The first discount can be modeled by $f(x)=x-15$. The second discount can be modeled by $g(x)=0.9x$. Here the second one is applied first and $x=85$, hence we are looking for: $f(g(85))=f(0.9(85))=f(76.5)=76.5-15=61.5$