To get x on its own, you times the 3 over to the other side so the 3 cancels out on the LHS.
~ x greater than or equal to -18
(C)
Answer:
10000 V
0.00225988700565 m²

Explanation:
E = Electric field = 
d = Gap = 2.5 mm
Q = Charge = 80 nC
= Permittivity of free space = 
Potential difference is given by

The potential difference between the plates is 10000 V
Area is given by

The area of the plate is 0.00225988700565 m²
Capacitance is given by

The capacitance is 
True.
Depending how accurate the graph is plotted
Explanation:
F net of sled = Tension force by rope - Kinetic friction between ground.
F normal of sled = mg = (67kg)(9.81kg/m^2) = 657.27N.
Kinetic friction = 0.18 (I cannot see the value) * Normal force of sled = 0.18 * 657.27N = 118.31N
So F net of sled = 800N - 118.31N = 681.69N.
(I cannot see what the question is asking for, please check on your own!)