9700/13 Biology Oct Nov 2021 Online Test | Cambridge AS and A Level MCQ

The diagram shows a graduated slide, with divisions of 0.1 mm viewed using an eyepiece graticule.
Pollen grains were grown in a sugar solution and viewed using the eyepiece graticule. Diagram 1 shows the pollen grains at first and diagram 2 shows them after four hours.
What is the growth rate of the pollen tubes?