Answer :
[tex]x+y=9 \\
0.5x+0.2y=3.15 \ \ \ |\times (-2) \\ \\
x+y=9 \\
\underline{-x-0.4y=-6.3} \\
y-0.4y=9-6.3 \\
0.6y=2.7 \\
y=\frac{2.7}{0.6} \\
y=\frac{27}{6} \\
y=\frac{24}{6}+\frac{3}{6} \\
y=4\frac{1}{2} \\ \\
x+y=9 \\
x+4 \frac{1}{2}=9 \\
x=9-4\frac{1}{2} \\
x=4\frac{1}{2} \\ \\
(x,y)=(4\frac{1}{2},4\frac{1}{2})
[/tex]
