To find how many pounds of oranges Marco can buy we need to solve the equation given:
[tex]\begin{gathered} 1.29(4)+0.79x=9.11 \\ 5.16+0.79x=9.11 \\ 0.79x=9.11-5.16 \\ \text{0}.79x=3.95 \\ x=\frac{3.95}{0.79} \\ x=5 \end{gathered}[/tex]Therefore Marco bought 5 pounds of oranges.