For large values of three, and small values of pi.
If you don't need the accuracy (was that temperature 12 000 000 C or 12 000 000 K?), and can get away with an approximation to an OrderOfMagnitude?, pi = 3 and pi^2 = 10.
Or rather pi^2 = g; cancels out nicely in physics courses. But for such approximations, g also equals 10. :-)
See also ValueOfPi"The value of 'pi', recited to the length of one decimal digit...