We have that the plant start with 5 cm high and it grows 1.5 cm per day, then the equation to model this situation is:

where x represents the days that passes and y represents the height of the plant.
Now, let's convert 30.5 inches to cm:
![\begin{gathered} 1in=2.54\operatorname{cm} \\ \Rightarrow(30.5)\cdot(2.54)=77.47\operatorname{cm} \end{gathered}]()
then, suppose that Lynn's plant grew to a height of 77.47 cm, then we have to make y = 77.47 and solve for x to get the following:

therefore, it will take approximately 48 days to the plant to grow to a height of 30.5 inches