title: Calculate point on a line if the slope is known
body: <p>Trying to compute the left and top of a page element.</p>
  
  <p>The element needs to be positioned on an imaginary line that runs from 0,0 of the page window to a point (roughly) equal to 425 pixels from the beginning of the line.</p>
  
  <p>The slope of the line is -.375.</p>
  
  <p>How can I calc the left and top using php?</p>