This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Anaesthesia
An, 8 year old boy, weighing 30kg is undergoing resection of wilms tumor. His hemoglobin is 12g/dL. If the threshold for transfusion is 8g/dL, the allowable blood loss is 
Select and explain. 
A. 820ml, B. 840ml, C. 860ml, D. 880ml
B: 840ml
Answer: B: 840ml 
Explanation: None