Sound level in room vs. number of people

I am having a little difficulty solving a problem, can you please help? The question is: The sound level in a room of 35 people talking is 63dB. How many people must leave the room to lower the sound level to 57 dB? Assume that all the people are speaking at the same intensity.

A system of point charges

Four charges are placed at the corners of a square, where q is positive. Initially there is no charge in the center of the square. 1) Find the work, W required to bring the charge Qf from infinity and place it at the center of the square. 2) Find the magnitude of the electric force on the charge q when it is placed at the center of the square. 3) Find the magnitude of the total electrostatic energy of the system, U. 4) What is the sign of the total energy associated with the five point charges.

electron problem

A voltage of 9 V is applied across the ends of a piece of copper wire 11 cm long. Given me = 9.11 x 10-31 kg and qe = -1.6 x 10-19 C. 1) What is the electron's acceleration in m/s2 ? 2) What is the speed of the electron after traveling 4 x 10-11 m, if it does not collide with a copper ion over this distance, in m/s? 3) What is the kinetic energy of the electron when traveling at this speed, in J? 4) What is the kinetic energy of the electron in eV when traveling at this speed, in eV?

potential problem

An infinite sheet of charge that has a surface charge density of 28 nC/m2 lies in the yz plane, passes through the origin, and is at a potential of 0.8 kV. A long wire having a linear charge density of 116 nC/m lies parallel to the y axis and intersects the x axis at 2m. What is the potential energy of a 3.2 nC charge placed at x = 0.5 m in units of nJ.

Electric field

1) Given: V = αx2y2 + βz2(x2 - γ) + δy3z Where α = 5 V/m4, β = 6.6 V/m4, γ = 3.4 m2, and δ = 5.3 V/m4. What is the y component of the electric field Ey at (4.6m, -4 m, 4.7 m)? Answer in units of V/m. 2) The electric potential in a certain region is: V = ax2 + bx + c, Where a = 10 V/m2, b = -19 V/m, and c = 55 V. Determine the electric field at x = 3 m. Answer in units of V/m.