The formula for gradient of the straight line is given by:
m = (y2 - y1)/(x2 - x1); where (x1, y1) and (x2, y2) are two fixed points on the straight line. It is given that (x1, y1) = (4, r) and (x2, y2) = (r, 2). The gradient of the straight line is given by -5/3. To find the value of r, simply substitute all the values in the gradient equation. Therefore: