[tex]\begin{gathered} \text{ If "x" = cost of }ft^2,\text{ of grass and y = cost of shrubs, then } \\ 2x+6y=72 \\ 6x+12y=156 \end{gathered}[/tex]
We must solve this sistem of equations, if we multiply the first equation by 3, we get
[tex]\begin{gathered} 6x+18y=216 \\ 6x+12y=156 \end{gathered}[/tex]
Now, we will do the first equation minus the second (side by side), so we have
[tex]\begin{gathered} (6x+18y)-(6x+12y)=216-156 \\ 18y-12y=60 \\ 6y=60 \\ y=\frac{60}{10}=6 \end{gathered}[/tex]
Replacing y =6 in the first equation we have
[tex]\begin{gathered} 2x+6(6)=72 \\ 2x+36=72 \\ 2x=72-36 \\ 2x=36 \\ x=\frac{36}{2} \\ x=18 \end{gathered}[/tex]
Thus each ft^2 of grass costs $18, and eachshrub costs $6.
