Whatever numbers you fill in (for x and y), in this formula, it is only correct when their sum is 4. Therefore the graph x + y = 4 is a line joining the points whose x and y coordinates add up to 4. The fourth answer is correct.
You can put the equation into standard form by subtracting x on both sides to get:
y = -x + 4
This graph has a negative 1 slope and is translated 4 units above the origin. Because the slope is -1, it will intercept the x - axis at 4 units and intercept the y - axis at 4 units as well.
The correct answer is D) It is a line joining the points whose x and y coordinates add up to 4
