Addition and subtraction of rational numbers~ When a > 0, b > 0, then a + B = + (___ +___ ) When a > 0, b > 0

Addition and subtraction of rational numbers~ When a > 0, b > 0, then a + B = + (___ +___ ) When a > 0, b > 0

The first question is a mess. I can't understand it. Maybe it's (1) a, B
(2)-a,b
(3)a,-b
(4)-a,-b
2. There are four situations
a,m=2,n=3
b,m=-2,n=3
c,m=2,n=-3
d,m=-2,m=-3
Third, add the first column - 6-11-4 = - 21
On the diagonal, - 6-7 + x = - 21
x=8