The equation that can be used to represent the situation given in the question is
t - 15.2 = - 12.8.
The correct answer to all the options given in the question is option "a". In the question it is given that a certain temperature "t" has decreased by 15.2 degree centigrade to finally reach a temperature of -12.8 degree centigrade. So the 15.2 degree centigrade needs to be deducted from the initial temperature of "t" degree centigrade. Then only the final temperature of -12.8 degree centigrade can be reached.