In the problem they are telling us that the graph shows the relationship between the number of yards of string and the number of bracelets made so in the graph y represent the yards of string and x represent the bracelets made so and the ratio can be calculate like:
So the ratio is:
so with 6 yards os string made 4 bracelets
and the point (6,9) rpcan be represent with the ratio
and this means that with 9 yards of string we can made 6 brecelets