Step 1:
Write the coordinates in terms of cost and number of days.
( cost , days )
Step 2
( 3 , 122 ) and ( 6, 194)
Step 3:
Find the slope
[tex]\begin{gathered} \text{Slope m = }\frac{y_2-y_1}{x_2-x_1} \\ x_1\text{ = 3} \\ y_1\text{ = 122} \\ x_2\text{ = 6} \\ y_2\text{ = 194} \\ m\text{ = }\frac{194\text{ - 122}}{6\text{ - 3}} \\ m\text{ = }\frac{72}{3} \\ m\text{ = 24} \end{gathered}[/tex]Step 4
Find the equation using the slope m and point 1
[tex]\begin{gathered} m\text{ = }\frac{y-y_1}{x-x_1} \\ 24\text{ = }\frac{y\text{ - 122}}{x\text{ - 3}} \\ \text{y - 122 = 24(x - 3)} \\ \text{y - 122 = 24x - 72} \\ y\text{ = 24x - 72 + 122} \\ y\text{ = 24x + 50} \end{gathered}[/tex]Final answer
The equation is y = 24x + 50
