Chapter 1 - 1.3 - Modeling with Linear Equations - 1.3 Exercises - Page 99: 56

$450000$ dollars was invested in minivans, and $150000$ dollars was invested in alternative-fueled vehicles.

Let $x$ be the amount invested on minivans. Then the amount invested on alternative-fueled vehicles is $600000-x$. Then our equation is: $0.24x+(600000-x)\cdot0.28=600000\cdot0.25\\0.24x+168000-0.28x=150000\\-0.04x=-18000\\x=450000.$ $450000$ dollars was invested in minivans, and $150000$ dollars was invested in alternative-fueled vehicles.