See the task is easier here than if the grammar were given and then asked that which operator has more precedence.But here we can answer about the precedence by simply examining the dervation tree.The behaviour is similar to recursion tree if you recall
According to the tree , we know that calling is done in top down manner but execution is done in bottom up manner.So the '-' being lower in the tree will be executed first then the '+' which is at higher level.
So '-' has higher precedence than '+'.
Hence C) is correct option.