Please explain the diagram and the formula?

Fig. 5.5 The long-run adjustment of capital stock per effective worker 1 K f' ( k ) _8 1+/ The determination of k is illustrated in Fig. 5.5. You will notice that this is the same diagram as Fig. 5.1. The only difference is that we now have capital per effective worker on the horizontal axis. If the stock of capital per effective worker is low, the return to investment is high, and the capital stock per effective worker will increase towards the steady state level. If the stock of capital per effective worker is high, the return to investment is low, and the capital stock per effective worker will decrease. In the steady state we have K Y EN =k* and EN =f (k. ) , or, alternatively, K* =KEN and Y* =f (k.) EN. The long-run levels of capital and output are proportional to employment. Because of constant returns to scale, production per capita in the steady state is independent of the size of the population