Potential difference between two points?

[bigbird24]

This is a question from my highscool gr12 physics class
Q) Two parallel plates are 8cm apart and are appositely charged. The electric potential difference across the plates is 160V. Point A is 2cm from the positive plate, point B is 3 cm from the negative plate.
-What is potential difference between points A and B

My attempt-
Electric field intensity: E=$$\Delta$$V/d = 160/0.08 =2000N/C
$$\Delta$$Va =E*d ---What value for d do i use?
$$\Delta$$Vb =E*d ---What value for d do i use?
$$\Delta$$Vab = $$\Delta$$Vb - $$\Delta$$Va

 

[zhermes]

because you're looking for potential difference you don't need to calculate the reference voltages at a and b independently. What if you just used
$$E = d \Delta V$$
straight from a to b?

 

[AJ Bentley]

You don't need formulae, you can do it in your head.

The plates are 8cm apart so at 160V there is a 20 volts per centimetre gradient between them.
The points are 3 cm apart so the answer is 60 volts.

 

[bigbird24]

thanks AJ, that makes sense to me