How much thrust is required to launch a 5 kg bottle rocket with an upward acceleration of 6.4 m/s2?

I've gotten 32 because F=MA but I don't understand how to account for gravity. Please help!

g + a = 6.4

-9.8 + a = 6.4
a = 6.4 + 9.8 = 16.2 m/s^2

Thrust = M*a = 5 * 16.2 = 81 N.