Sentence:  Now, after having solved the <WSD>biannual</WSD> period problem back to period one of the ten <WSD>biannual</WSD> periods, i.e. quarters 77–84 it is necessary to convert the state variables, namely "n", "SK" and "GK", from <WSD>biannual</WSD> to annual units. 
Meaning of the word marked with <WSD> tags:  Occurring once every two years; biennial.