Let:
[tex]\begin{gathered} k=\text{constant of proportionality:} \\ y=kx \\ for\colon \\ x=2 \\ y=3 \\ so\colon \\ 3=2k \\ \text{solve for k:} \\ k=\frac{3}{2}=1.5 \end{gathered}[/tex]----------------------------------------------------------------
Let:
x = Number of hours
Let:
[tex]\begin{gathered} (x1,y1)=(4,58) \\ (x2,y2)=(6,87) \\ k=\frac{y2-y1}{x2-x1}=\frac{87-58}{6-4}=\frac{29}{2}=14.5 \\ y-y1=m(x-x1) \\ y-58=\frac{29}{2}(x-4) \\ y-58=\frac{29}{2}x-58 \\ y=\frac{29}{2}x \end{gathered}[/tex]