And how?
Here's a repersentation of the Sun on our flat Earth model.
With trig, we get:
Using the values 50 degrees and 60 degrees as measured on the trip, with b=1000 miles, we find that h is approximately 2000 miles. We also find that a is approximately 2400 miles and the two distances R1 and R2 are approximately 3000 and 3900 miles, respectively.
This is solid math that supports flat Earth.
As for other evidence, simply look outside.