What does the line 2x + y = 7 look like?

Well let's take a look at it and see..
First month let's put the equation in slope intercept form.. that looks like
y=mx+b

2x + y = 7

y = -2x + 7

So now we have a slope of -2 and a y intercept of 7.

Set a couple of x coordinates and solve for y...

When x is 0,
y = -2x +7
y= 0+7= 7
so one point is (0, 7)

When x is 1,
y= -2(1) + 7= 5
So another point is (1, 5)

Use the points to graph the line... see the pic.