6. Write down the posterior Pr(QO)=Pr(O)Pr(OQ)Pr(Q) estimated by HMM for an observed sentence O= [o1,,oT] and a sequence of POS tags Q=[q1,,qT]. You need to fully specify the likelihood Pr(OQ), the prior Pr(Q), and the marginal Pr(O). Then explain the time complexity for calculating the marginal