To get the speed of growth of plant we proceed as follows;
rate=(distance)/(time taken)
distance( length) of growth of the plant in 14 days is 3.6 m.
1 day=86400 sec
14 days=86400x14=1,209,600 sec
1 m=1000000 micrometer
3.6 m=3600000 micrometer
thus the rate of growth will be:
3600000/1209600
=2.9762 micrometers per second