Transitional parameter using threshold

[Aurasphere]

Hi
This is probably so simple but I never did well with maths at school and have to solve this programatically
I have a constant: a threshold value of 600mm
I need to find the position along the baseline at where this threshold intersects etc.
ie at what point along a will the 600mm be?
Pictures speak...please see attached... the second figure represents encountered variations

 

[LCKurtz]

Measuring [MATH]x[/MATH] positive to the right and [MATH]y[/MATH] positive downward and the origin at the upper left corner, you want the equation of the straight line between [MATH](0,400)[/MATH] and [MATH](2500,1400)[/MATH]. Let [MATH](x,y)[/MATH] be a variable point on that line. Then using slope = slope:
[MATH]\frac{y-400}{x-0} = \frac{1400-400}{2500-0}[/MATH]Can you take it from there to solve it for [MATH]x[/MATH] in terms of [MATH]y[/MATH]? Then put in [MATH]y=600[/MATH] and you will have your [MATH]x[/MATH]. And it would work for any other [MATH]y[/MATH] too.

 

[Aurasphere]

@LCKurtz thanking you very much