P=F/A
Force= P * A = (2000 x 3) N = 6000N
(a) 
According to Newton's second law, the force experienced by each balloon is given by:
F = ma
where
m = 0.021 kg is the mass
a = 1.1 m/s^2 is the acceleration
Substituting, we found:

The electrostatic force between the two balloons can be also written as

where
k is the Coulomb's constant
Q is the charge on each balloon
r = 16 m is their separation
Since we know the value of F, we can find Q, the magnitude of the charge on each balloon:

(b)
electrons
The magnitude of the charge of one electron is

While the magnitude of the charge on one balloon is

This charge can be written as

where N is the number of electrons that are responsible for this charge. Solving for N, we find:

A. 2 C₂ H₆ + 7 O₂ → 4 C O₂ + 6 H₂ O
according to law of conservation of mass , the total mass of reactants side must be same as the total mass of product side. so we need to check if each atom in the equation has same number on both side of the equation or not.
in this equation , we have
4 atoms of carbon left and 4 atoms of carbon on right
12 atoms of hydrogen on left and 12 atoms of hydrogen on right
14 atoms of oxygen on left and 14 atoms of oxygen on right
Acceleration is the change in velocity