To determine the time it will take Jeff to read 90 pages, the first step is to calculate the rate of change using the formula of the slope
[tex]m=\frac{y_2-y_1}{x_2-x_1}[/tex]
Using the points (1,20) and (3,60)
[tex]\begin{gathered} m=\frac{60-20}{3-1} \\ m=\frac{40}{2} \\ m=20 \end{gathered}[/tex]
This means that Jeff reads 20 pages per hour.
The relationship between both variables is direct
[tex]\begin{gathered} y=mx \\ y=20x \end{gathered}[/tex]
Using this expression you can calculate the time it will take him you read 90 pages, replace the equation with y=90
[tex]90=20x[/tex]
Divide both sides by 20
[tex]\begin{gathered} \frac{90}{20}=\frac{20x}{20} \\ 4.5=x \end{gathered}[/tex]
It will take him 4.5 hours to read 90 pages.
