Question

Find the equation of the line I in the following picture. The shapes under the lines are squares

Answer 1

If you look carefully at the graph, you may see that the slope of the line is
          3-4           -1
---------------- = ------ = m
         7-4             3

thus, you have the slope of the line and two points on the line.  Suppose we
choose the point (4,4) and subst. the known slope and the coordinates of this point into the point-slope formula for the eqn of a str line:

y-y1 = m (x-x1)

y-4 = (-1/3)(x-4)

This is the desired equation.  You could, if you wished, change this into slope-intercept form.