Rate of Rxn? Chemistry Help???

Question

Consider the following set of data ccollected for a reaction of the form

A --> products.

time (seconds)	[A] (M)
0	1.000
10	0.641
20	0.472
30	0.373
40	0.309
50	0.263

 

What is the average rate of the reaction between 30 and 40 seconds?

rate = ___ M/s