How do you find out that price is $20 and price of labor is $10 based off this graph?? i am confused

The expansion path shows the cost-minimizing input combination for each level of output with the input price ratio held constant. It therefore shows how input usage changes as output changes. Figure 9.6 illustrates the derivation of an expansion path. Isoquants @1. 22. and @3 show, respectively, the input combinations of labor and capital that are capable of producing 500, 700, and 900 units of output. The price of capital (r) is $20 and the price of labor (w) is $10. Thus any isocost curve would have a slope of 10/20 = 1/2. FIGURE 9.6 An Expansion Path K" 250 K' 200 Expansion K C Capital (K) path 150 B 126 Q3 = 900 A 91 Q2 =700 Q1 = 500 L L' O 118 148 200 300 400 500 por (L)