when $X_{min}=50, Y_{min}= 1.0$
when $X_{max} > 50, Y_{max}= 1.5$, where $X_{max}$ varies from $51, 52, 53, \ldots$
What is the value of $Y$ at any given point fo $X$? If $X_{min}$, $X$ & $X_{max}$ are plotted should produce a straight line.
How to calculate $Y$?
What I tried,
$$Y = \frac{(X)(X_{max} - X_{min})}{(Y_{max} - Y_{min})}$$
If I well understand you want a stright line that pass thorough the pont $P=(x_m,y_m)=(50,1)$ and a point $P'=(x_M,y_M)=(x_M,1.5)$ with $x_M>50$.
This line has equation: $$ y-y_m=\dfrac{y_M-y_m}{x_M-x_m}(x-x_m) $$
So for every value of $x_M$ you have a differnt stringt line:
$$ y-1=\dfrac{1.5-1}{x_M-50}(x-5) $$