Let's find the top line first, so it has x intercept -1 and y intercept 1 so y = x+1
Now the bottom line has gradient -1/2 and y intercept 1 so y = -x/2 + 1
The vertical line is x = 3
Now it's under the top line, on top of the bottom line and left of the vertical, so:
y<= x+1
y>= -x/2 + 1
x<=3