A city is planning to build a retaining wall using Basalt, Granite, and Limestone. The table below shows four rock types that will be considered for use in the project. Also shown for each rock type is its weight per volume, in pounds per cubic foot (lb/ft), and the cost per pound, in dollars.
| Rock type | Weight per volume (lb/ft) | Cost per pound |
|---|---|---|
| Basalt | 180 | 0.09 |
| Limestone | 120 | 0.22 |
If cubic feet of Basalt, cubic feet of Granite, and cubic feet of Limestone are used in the retaining wall, which of the following equations represents the total cost , in dollars, for the rocks used?
