Read this and answer the question. If the question is unanswerable, say "unanswerable".

The decade began with the Melbourne International Exhibition in 1880, held in the large purpose-built Exhibition Building. In 1880 a telephone exchange was established and in the same year the foundations of St Paul's, were laid; in 1881 electric light was installed in the Eastern Market, and in the following year a generating station capable of supplying 2,000 incandescent lamps was in operation. In 1885 the first line of the Melbourne cable tramway system was built, becoming one of the worlds most extensive systems by 1890.

In what year was the first line of the Melbourne cable tramway system built?
1885