Answer:
Step-by-step explanation:
If it's a linear, then
[tex]\dfrac{y_2-y_1}{x_2-x_1}=constant[/tex]
Substitute the values from the table:
[tex]\dfrac{70-60}{5-1}=\dfrac{10}{4}=2.5\\\\\dfrac{80-70}{20-5}=\dfrac{10}{15}=\dfrac{2}{3}[/tex]
[tex]2.5\neq\dfrac{2}{3}[/tex]