(a) To find the probability that Davin plays for more than 4.2 hours, we use the standard normal distribution. First, we standardize the variable:

\(P(X > 4.2) = P\left( Z > \frac{4.2 - 3.5}{0.9} \right) = P(Z > 0.7778)\)

Using the standard normal distribution table, \(P(Z > 0.7778) = 1 - 0.7818 = 0.218\).

(c) To find the number of days Davin plays between 2.8 and 4.2 hours, we calculate:

\(P(2.8 < X < 4.2) = 1 - 2 \times P(X > 4.2)\)

\(= 2 \times (1 - 0.7818) - 1 = 2 \times 0.2182 - 1 = 0.5636\)

The number of days is \(365 \times 0.5636 = 205.7\), so approximately 205 days.