Construction of the model:
GDP = 577 * (1.032) ^ t, where GDP is in billion dollars and t is the time in years since 1985.
year     t (in years)   GDP (in billion dollars)
1985    0                   577
1986    1                   577* 1.032 = 595.46 
1987    2                   577 * (1.032)^2 = 614.52
1988    3                   577 * (1.032)^3 = 634.18
?           t                   577 * (1.032)^t
Then, GDP = 1.8 trillion = 1800 billion = 577 * (1.032)^ t
=> (1.032)^t = 1800 / 577
=> t log (1.032) = log (1800 / 577) 
=> t = log (1800 / 577) / log (1.032) = 36.12
Therefore, if the growth rate keeps in 3.2% per year, the GDP will equal 1.80 trillion 36 years after 1985 => 1985 + 36 = 2021.
Answer: 2021