I'm not sure if this is the correct forum to post this thread in. Does anybody know how to interpolate? The numbers below are from a runway analysis landing chart. In the instructions I was given, they somehow got 195.000 pounds as the approach climb limit with an outside air temperature of 8 degrees Celsius. What is the actual formula for getting this answer?

Temp (c): -20 / 19
Climb WT: 209.1 / 190.0

Temp (c): -20 / 19
Climb WT: 209.1 / 190.0

I think I more or less figured it out with the six step process below:

Its not exactly 195,000 pounds but its pretty close, which means I must be doing something right.