Although the question is incomplete, I have seen it before.
The equations are:
3a + 6b = 12
-3a + 6b = -12
Adding the equations, we get:
12b = 0
And b = 0
I don't know if I understand this question that well, but if I am right, the first digit of the question you are asking is 5, and it is in the hundreds place. If this is not what you mean, then can you put more description in this question please?
For the red line, we have:
gradient (

) = 1/3
y-intercept = 3
Equation of straight line is given by

, where

is the gradient and

is where the line intercept the y-axis
So we have,

The shaded part is above the line, hence the first inequality is

The black line, we have
gradient,

= 3
y-intercept = -2


, rearranging gives

The shaded region is to the right of the line, hence the inequality is

Note: The first option should be the correct answer but the inequality sign for <span>y > 1/3x + 3 should be </span>
Answering from phone so this will be a bit messy.
a
b=a+1
c=b+1=a+2
2a=b+20
Therefore:
2a=a+1+20
a=21,b=22,c=23