Question 830107
You want the x intercept from a standard form equation of a line.
{{{Ax+By=C}}};


The x intercept is the point for y=0.
{{{Ax+B*0=C}}}
{{{Ax+0=C}}}
{{{Ax=C}}}
{{{highlight_green(x=C/A)}}}


Were you able to derive the equation for the line which the two given points define?  Which form for the equation you use would be less important.  Just solve for x, and let y=0, and compute.