Read this: Public expenditure of the GDP was less in 2002–05 than in 1991. Public education is theoretically free and mandatory for under-16-year-olds, but in practice, expenses exist. Net primary enrollment rate was 44% in 2005, much less than the 79% in 1991. The country has universities. Education between ages six and sixteen is compulsory. Pupils who complete six years of primary school and seven years of secondary school obtain a baccalaureate. At the university, students can obtain a bachelor's degree in three years and a master's after four. Marien Ngouabi University—which offers courses in medicine, law and several other fields—is the country's only public university. Instruction at all levels is in French, and the educational system as a whole models the French system. The educational infrastructure has been seriously degraded as a result of political and economic crises. There are no seats in most classrooms, forcing children to sit on the floor. Enterprising individuals have set up private schools, but they often lack the technical knowledge and familiarity with the national curriculum to teach effectively. Families frequently enroll their children in private schools only to find they cannot make the payments.

When is education not compulsory?
What is the answer? (If it cannot be answered, return "unanswerable")
unanswerable