Hey there! So for this one, you would just have to divide the change in concentration by the change in time. You should put a negative sign in the numerator to get a positive value. Since this would initially give a negative value (negative rate)if you don't which is only natural since it is a disappearance. So solving for the rate :
-(M2-M1)/(t2-t1) = -(0.073-0.110)/(30-10) = -0.037/20 = 0.00185 M/s
So the answer should be A.
I hope this helps!