The graph shows a parabola with vertex at (0,9). It opens down. This is sufficient info with which to write a quadratic equation for temperature as a function of time: T(t) = -t^2 + 9.
It happens that we want to know the times at which T=8 degrees F. To do this, set T(t) = -t^2 + 9 = to 8 and solve for t:
-t^2 + 9 = 8, or 1 = t^2., or 9 - t^2 = 8.
While we were not asked to find these times, doing so is easy: t = plus or minus 1.
