The height of the plant, y, after x days could be modeled by the equation
<h3>y-y0=k(x-xo) (1),</h3><h3>where y0 was the initial height at 'x0'th. day, and k is the constant of proportionality.</h3><h3>From equation (1), k could be evaluated as follows:</h3><h3>k=(y-y0)/(x-x0) </h3><h3>From the problem statement, we may determine k by plugging in the given values, e.g. y0= 35, x0=10, y=55, x=20.</h3><h3>Thus,</h3><h3>k=(55-35)/(20-10)=2</h3><h3>Therefore, the model equation becomes</h3><h3>y-35=2(x-10)</h3><h3></h3>