B is the correct answer.
This is because the numbers in the parentheses have a negative sign in front of them. If you have an equation that "subtracts" a negative number, the sign would change to the opposite and you would have to add. To avoid that, you have to put an addition sign to subtract correctly.
✅70+(-9)+(-7)=70-9-7
❌70-(-9)-(-7)=70+9+7
