You must have copied the figures wrongly. 102/300 does not equal 0.0343! It is equal to 0.34.
r is the third root of 0.34, which is 0.70
How you take the third root depends on your calculator (you need a scientific calculator) – different calculators have different buttons. You will need to check in the manual – if you have lost it then search on Google by entering the model number and you will find it.