If you mean Pi instead of n, then that's the formula for the surface area of a cylinder.
S = 2 * Pi * r * h + 2 * Pi * r^2
1221 = 2 * Pi * 10.5 * h + 2 * Pi * 10.5^2
1221 = 21 * Pi * h + 220.5 * Pi
1221 - 220.5Pi = 21Pi * h
h = (1221 - 220.5Pi) / 21Pi
h = (1221 - 692.7212) / 65.9734 (note: numbers are approximate due to Pi)
h = 528.7288 / 65.9734
h = 8.0075
h = about 8