Chapter 6 - Systems of Equations and Inequalities - Mid-Chapter Quiz - Page 389: 12

$x=15, y=-.5$

$3x+6y = 42$ and $-7x + 8y= -109$ $3x+6y = 42$ $7/3*(3x+6y = 42)$ $7x + 14y = 98$ $(7x + 14y) + (-7x + 8y) = (98-109)$ $22y = -11$ $22y/22 = -11/22$ $y = -1/2$ $3x+6y=42$ $3x+6*(-1/2) = 42$ $3x - 3 = 42$ $3x-3+3 = 42+3$ $3x = 45$ $3x/3 = 45/3$ $x = 15$