The length of the pool would be 8.5 x 4.5 = 38.25 meters.
Using the Pythagorean theorem the diagonal is:
Diagonal = sqrt(38.25^2 + 8.5^2)
Diagonal = 39.183 meters
You swim it 6 times.
Total distance = 39.183 x 6 = 235.098 meters.
Round to 2 decimals = 235.10 meters