Write the equation of the line in fully simplified slope-intercept form.

-1x+8

If you pick a point on the line and see the height difference and distance of the next point (from left to right) you can find the slope. You must go down 1 (-1) and over 1 which gives this line a slope of -1/1 which equals -1.

Next we find the y-intercept which is much easier. Find what point on the y-axis (vertical bold line) the line passes. It passes at 8 so the y-intercept is 8.

Now to make the equation we multiply the slope with x and add the y-intercept.

-1x+8

i'm assuming it's looking for the missing length, which should be 4cm

hope this !