Keren faces a progressive tax structure that has the following marginal tax rates: 0 percent on the first $10,000, 10 percent on the next $10,000, 15 percent on the next $10,000, 25 percent on the next $10,000, and 50 percent on all additional income. If Keren earns $50,000 per year, what would be her tax liability?

Can you please elaborate or explain how you can get her tax liability? That would be much appreciated.