Step 1 :Find the decimal approximation of \(\sqrt{7}\) by taking the average of the square roots of the lower and upper bounds: \(\frac{\sqrt{6.9} + \sqrt{7.1}}{2} \approx 2.6457\)
Step 2 :Divide the thickness of the graphite by the thickness of a single layer of graphene to find the number of layers: \(\frac{0.0016}{2 \times 10^{-10}} = 8 \times 10^6\)
Step 3 :boxed{Question 3: 2.6457}
Step 4 :boxed{Question 4: 8 \times 10^6}