January 2012 Rings, Polymers and Analysis Q4,C HELP

So my question is about realising the structure, so far this the information i have, but i don't understand why there are three CH3 groups? How exactly do you knw this?So far Mass= 144 so C8H16O2Quartet so adjacent carbon has a CH3 methyl groupSinglet so adjacent carbon has no hydrogens so likely the C=0Triplet so adjacent carbon has two hydrogens -CH2Singlet so adjacent carbon has no hydrogens so likely the C--0But how do you figure out there a three methyl groups in the ester i looked at the examiners report and this is a common mistake? The mark scheme gives no explanation is the area of the peak is three times another peak ???Link to Question:http://pmt.physicsandmathstutor.com/download/Chemistry/A-level/Past-Papers/OCR-Old/Unit-4/January 2012 QP - Unit 4 OCR Chemistry A-level.pdf Question 4C