Please explain this graph step by step in good details, what does it mean, where did the slope come from? thanks

FIGURE 11.10 The lsocost Line For given input prices (r = 2 and w = 4 in the diagram), the isocost line is the locus of all possible input bundles that can be purchased for a given level of total expenditure C (6200 in the diagram). The slope of the isocost line is the negative of the input price ratio, - w/r