Deriving the Learning Rate using the Tabular Approach.

Question: The first batch of 10 units will take 300 labour hrs. The total time for the first 16 batches will take 3300 hrs. What is the actual learning rate to the nearest %.

Sir if i am correct, i know that the question boils down to the following equation:
16*300r4=3300
r4=3300/4800
=0.6875
r=

My problem sir is that i don’t know how to enter the 0.6875 in my scientific calculator to ascertain the learning rate. Kindly say which is the button i need to use.