Since the elongation E varies directly with the weight W, they are related as follows
[tex]E=kW[/tex]
where k is the constant of proportionality. In order to find k, we can substitute the given values, that is, when E=2, W=15, then we have
[tex]2=k\cdot15[/tex]
Then, k is given as
[tex]k=\frac{2}{15}[/tex]
Therefore, our formula for any E and W is
[tex]E=\frac{2}{15}W[/tex]
Now, in order to find E in the second case, by replacing W=10, we get
[tex]E=\frac{2}{15}(10)[/tex]
which yields
[tex]E=\frac{20}{15}=\frac{4}{3}[/tex]
Therefore, the answer is
[tex]E=\frac{4}{3}[/tex]
