Question

how do I find the value of the constant of variation for Nikiya's plan

Answer 1

The variation for Nikiya's plan is the slope of the linear function of the Phone Plan Cost.

In the picture we can see that the point (0, 0) and (2, 30) belongs to Nikiya's Cost (blue line), so the slope is:

$\begin{gathered} P1=(x_1,y_1)=(0,0) \\ P2=(x_2,y_2)=(2,30) \\ \text{The slope m is:} \\ m=\frac{(y_2-y_1)}{(x_2-x_1)}=\frac{30-0}{2-0}=\frac{30}{2}=15 \end{gathered}$

The constant of variation is 15 $/hours