Deceleration isn't a term in physics; you can have positive acceleration which is speeding up and negative acceleration which is slowing down
Use newton's law F = ma
a = F/m
Explanation:
Given: uniform electric field E= 82.0 kN/C.
a) charge density σ =ε_0 E.
therefore, 
b)Total charge on each face = σA
q=σA

3.60 A = 3.60 coulombs of charge per second
(3.60 Coul/sec) x (15.3 sec) = 55.08 coulombs of charge
1 coulomb of charge is carried by 6.25 x 10^18 electrons
Number of electrons =
(55.08 Coul) x (6.25 x 10^18 e/coul) = <em>3.4425 x 10^20 electrons</em>