Formula (how to calculate) Y axis cross-point of two intersecting lines i.e. I have two lines:

A) Orange (Y axis starts at: 6,  end at: -3)
B) Green  (Y axis starts at: 5,  end at: -2)
the start/end X axis values are same. Please note, I don't have SLOPE(angle) information, we only know what I've mentioned.
How to calculate (what formula to use) to get the cross-point Y value?  it's about 0.8 estimately (as I see visually), but what is the formula I cant reach...  I've tried so far:
mid_orange = (orange_start_Y + orange_end_Y )/2
mid_green  = (green_start_Y  + green_end_Y  )/2
cross_point_Y= (mid_orange *m + mid_green *n )/2

I think I need correct m and n coefficients... I don't know...

I've also successfully used this formula:
xCoef = (orangeStartY - greenStartY)/(greenEndY-greenStartY-orangeEndY+orangeStartY)
CrossPointY = xCoef * (greenEndY-greenStartY) + greenStartY

