Chapter 2 Linear Equations and Functions - 2.5 Model Direct Variation - 2.5 Exercises - Skill Practice - Page 109: 12

20

We plug in the given point to find the constant of variation. Since the equation will be for direct variation, we can then plug this in for $a$ in the equation $y=ax$. (Note, the y-intercept is 0). Hence, we find: $$ -5 = -3a \\ a =5/3$$ Thus: $$y=(5/3)x$$ When x=12: $$ y=\frac{5}{3}(12)=20$$