a.

Identify the unknown:

The potential difference between the plates

Step 3

List the Knowns:

Electric field: \(\displaystyle{E}={7.5}\times{10}^{{{4}}}\frac{{V}}{{m}}\)

Distance between the two plates: \(\displaystyle{d}={4}{c}{m}={0.04}{m}\)

Step 4

Set Up the Problem:

Potential difference between two uniform metal plates:

\(\displaystyle\Delta{V}_{{{A}{B}}}={E}{d}\)

Step 5

Solve the Problem:

\(\displaystyle\Delta{V}_{{{A}{B}}}={7.5}\times{10}^{{{4}}}\times{0.04}={3000}{V}\)