Answer
$1997$
The symmetry on the given chart does not hold when we move farther away from the $t=7$ line (beyond 0 and 14,) so the model would not be a good fit (would not give good approximations) for these values of t.
Work Step by Step
In years 6 and 8 (after 1990) we have the same expenditure value, ${\$} 800$ billion,
as we do for years 4 and 10 (${\$} 900$ billion),
and, also for years 2 and 12 ...
If we model the midpoints of the upper edges of the rectangles,
with a quadratic function, its graph would be symmetric (roughly) about the line $t=7.$
The vertex lies on the line of symmetry, so the year is 1997 (7 years after 1990.)
Extrapolating for farther values of t, the symmetry on the given chart does not hold any more, so the model would not be a good fit when we move too far away from 1997.
