On a cold January day, Mavis noticed that the temperature dropped 21 degrees over the course of the day to 9 degrees Celcius. Write an equation to determine what the temperature was at the beginning of the day.

-9 + 21 = t t = 12°C.

Step-by-step explanation:

For this problem lets have t be equal to the original temperature in the beginning of the day. The equation -9 + 21 = t represents this situation because it states that if we add the degrees that dropped to the current degrees  it will give us our original degrees. Solve. -9 + 21 = t (Simply add -9 + 21) -9 + 21 = (+12) 12 = t So, the original degrees in the beginning of the day was 12°C.