It takes $12.25$ hours for an airplane to fly from Shanghai to Los Angles. On the other hand, because earth spins in specific direction, it takes $90$ more minutes to fly from Los Angles to Shanghai. How many hours will it takes for a round-trip between the two location? 
Overseas Competition->Knowledge Point->Calculation Modules->Decimals->Addition and Subtraction of Decimals->Subtraction of Decimals