For each rated song, the Willingness$-$to$-$Pay $($WTP$)$ is as follows:

Rated $1$ Star $-$ WTP $$0\mathrm{.}10$

Rated $2$ Stars $-$ WTP $$0\mathrm{.}25$

Rated $3$ Stars $-$ WTP $$0\mathrm{.}50$

Rated $4$ Stars $-$ WTP $$0\mathrm{.}90$

Rated $5$ Stars $-$ WTP $$1\mathrm{.}50$