Answer:
{(x+12)° - 9°} - x°
Explanation:
Let the initial temperature be= x°
It increased by 12° between 9am and 12 = (x+12)°
It decreased by 9° between noon and 6pm= (x+12)° - 9°
change in temperature will be given by= temperature at 6pm -initial temperature
{(x+12)° - 9°} - x°