Explanation:

- Let's denote the temperature on Sunday as \( S \), on Monday as \( M \), on Tuesday as \( T \), and on Wednesday as \( W \).

- The average temperature of Sunday and Monday is \( 37.2^\circ C \):

\((S + M)/2 = 37.2\)

- The average temperature of Tuesday and Wednesday is \( 39.4^\circ C \):

\((T + W)/2 = 39.4\)

- The average temperature of Monday, Tuesday, and Wednesday is \( 38.1^\circ C \):

\((M + T + W)/3 = 38.1\)

- Solving the equations:

$$S + M = 74.4$$

$$T + W = 78.8$$

$$M + T + W = 114.3$$

- Substitute \( M = 74.4 - S \) into the third equation:

$$(74.4 - S) + 78.8 = 114.3$$

$$153.2 - S = 114.3$$

$$S = 153.2 - 114.3$$

$$S = 38.9^\circ C $$

- 38.9°C is the correct temperature for Sunday.