Answer: 25 pounds.
Explanation:
Let x represent the number of pounds of seeds that worth 80¢.
Let y represent the number of pounds of seeds that worth 50¢.
Based on the information given in the problem, you can set up the following system of equations:
![\left \{ {{x+y=30} \atop {80x+50y=75*30}} \right.\\\\\left \{ {{x+y=30} \atop {80x+50y=2250}} \right.](https://img.qammunity.org/2020/formulas/mathematics/high-school/zgm7wtcqakq5eyqui6sktctd4st8zhxot6.png)
Apply the method of elimination:
- Multiply the first equation by -50
- Add both equations.
- Solve for x.
Then:
![\left \{ {{-50x-50y=-1500} \atop {80x+50y=2250}} \right\\\\30x=750\\x=25](https://img.qammunity.org/2020/formulas/mathematics/high-school/yjvx0570ga30aprwgb2zqknf9ry96c4o5e.png)
Therefore, the answer is: 25 pounds of 80 cent seed should be use.