At x=3 the y output is 7.428. At x=5 the y output is 7.729. Since te rate of change is rise/run, run being the x, you know that it is (something) over 2. The rise would be the difference of the two y outputs. 7.729-7.428= 0.301. Therefore, 0.301/2 would be your answer. Checked by y=0.301/2x+6.975 - the two limes line up at x=3 until x=5 exactly.