Let the random variable representing petrol consumption be denoted by \(X\), where \(X \sim N(24, 4.7^2)\).

We need to find \(P(21.6 < X < 28.7)\).

Standardize the variable using the formula:

\(z = \frac{x - \mu}{\sigma}\)

For \(x = 21.6\):

\(z_1 = \frac{21.6 - 24}{4.7} = -0.5106\)

For \(x = 28.7\):

\(z_2 = \frac{28.7 - 24}{4.7} = 1\)

Thus, we need to find \(P(-0.5106 < z < 1)\).

This is equivalent to \(\Phi(1) - \Phi(-0.5106)\).

Using standard normal distribution tables:

\(\Phi(1) = 0.8413\)

\(\Phi(-0.5106) = 1 - \Phi(0.5106) = 1 - 0.6953 = 0.3047\)

Therefore, \(P(-0.5106 < z < 1) = 0.8413 - 0.3047 = 0.537\).