Chapter 4 - Section 4.3 - Solving Systems of Linear Equations by Addition - Exercise Set - Page 308: 41

$(-0.5, 2.5)$

$0.02x+0.04y=0.09$ $-0.1x+0.3y=0.8$ Multiply the first equation by 100 and the second equation by 10. $2x+4y=9$ $-x+3y=8$ Multiply the second equation by 2. $2x+4y=9$ $-2x+6y=16$ Add both equations. $10y=25$ $y=2.5$ Solve for $x$. $2x+4y=9$ $2x+4(2.5)=9$ $2x+10=9$ $2x=-1$ $x=-0.5$ $x=-0.5; y=2.5$ $(-0.5, 2.5)$