PMP Certification Executing Questions Test 6

A project's budget at completion (BAC) is US$\mathrm{\$}$100,000, its earned value (EV) is US$\mathrm{\$}$20,000, and its actual cost (AC) is US$\mathrm{\$}$10,000. The planned value (PV) is US$\mathrm{\$}$20,000.
What efficiency must be maintained to achieve the current estimate at completion (EAC)?