A city is planning a project that uses Basalt, Limestone, and Sandstone. 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 |
The total weight of the rocks for this project is 1,500 pounds. If 4 cubic feet of Basalt is used, and the cost of the Limestone used is equal to the cost of the Sandstone used, which of the following equations shows the relationship between the volumes, and , in cubic feet, for Limestone and Sandstone, respectively, based on the cost equality?
