The methyl groups are equivalent so produce one signal with integral 6, while the other protons both produce signals with integrals 1.
The student must recognise that all protons are detectable by NMR, including those attached to O atoms, and know how to count proton environments (COOH protons are sometimes too broad to detect due to proton exchange and/or hydrogen bonding, but this point is not covered at IB level).
The question is categorised as hard as several features of the NMR spectrum must be predicted.
