Answer:
Mrs. Khan is mailing 2 packages. Subtract 623 – 312 best describe how to find out how much heavier the larger package is. Hence Option C is correct
Solution:
Given that 
Mrs khan is mailing two packages. 
Weight of larger package = 623 pounds 
Weight of small package = 312 pounds 
Now we need to find how much heavier larger package compare to smaller one is. 
To get this if we remove weight of smaller package from larger package , we will get how much larger package is heavier. 
That is Weight of larger package – Weight of smaller package = 623 pounds – 312 pounds 
Hence option C) subtract 623 – 312 best describe how to find out how much heavier the larger package is.