Explanation:

- We have the mean temperatures for two periods: Monday to Thursday and Thursday to Sunday.

- The mean temperature from Monday to Thursday (4 days) is 39.25°C. Thus, the sum for these 4 days is 39.25°C × 4 = 157°C.

- The mean temperature from Thursday to Sunday (4 days) is 40.25°C. Thus, the sum for these 4 days is 40.25°C × 4 = 161°C.

- Thursday's temperature is counted in both sums. By adding both we include Thursday twice, once we subtract this double-count Sum we get overall correct sum:

$$

(157 + 161 - T) = 277.5 \rightarrow 318 - T = 277.5 $$

- Solving for T,

$$

T = 318 - 277.5 = 40.5°C $$

- 40.5°C is the correct answer.

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