Question: how to calculate the difference between a positive and negative number?
Answer: If the two numbers are on opposite sides of 0 (e.g., −5 and 2), then you add the absolute values (e.g., |−5|+|2|=5+2=7), or alternatively subtract the negative number from the positive one which effects a sign change (e.g., 2−(−5)=2+5=7).