A car has a mass 1230 kg and is on an icy driveway inclined at an angle of 39 degrees.

The acceleration of gravity is 9.8 m/s^2 . If the incline is frictionless, what is the
acceleration of the car?

I'm sure we're assuming an icy driveway to be "frictionless".

Basic equations are F = ma & W = mg & Fparallel = W sin theta

Find net force on the car:

Fparallel = F / m = W sin theta / m since W = mg we now have mg sin theta / m

m's cancel

so we are left with a = g sin theta = 9.8 m/s/s (sin 39) = 9.9 m/s/s (0.629 ) = 6.2 m/s/s down the driveway.