Do u see any similarities between the numbers? Both 12 and -4 have a variable(N). 8 and -7 dont have a variable, so u have to calculate them individually.
One thing to remember is just because there is a minus sign(-) or a plus sign(+) does not mean its addition or subtraction. its the value of the number. the sign to the left of the number is its value. so left of 12 is plus(+), so its a positive. left of 4 is a minus sign(-) so its a negative 4. lastly, left of 7 is minus sign(-), which means its negative 7. now u add.
