2023 Gauss 8 Problem 17

For 30 consecutive days, the daily high temperature was recorded. On each of the first 25 days, the temperature recorded was 21^\circC. On each of the remaining 5 days, the temperature recorded was 15^\circC. For the 30 days, the mean (average) of the temperatures recorded was

\textbf{(A)}\ 17^\circ\text{C}\quad \textbf{(B)}\ 19^\circ\text{C}\quad \textbf{(C)}\ 20^\circ\text{C}\quad \textbf{(D)}\ 16^\circ\text{C}\quad \textbf{(E)}\ 18^\circ\text{C}

If there are no answer choices shown, enter a numerical answer.

Full credit to this problem is given to the CEMC, you may view all Gauss contests here.