Providing that there is no friction acting on the surface, you want to resolve the forces in the x and y direction.
Remember to choose your x parallel to your plane and y perpendicular to the plane.
F(net,y) = N-mgcosx = 0 as the object does not accelerate into the plane, where x is the angle of inclination
F(net, x) = mgsinx = ma
Therefore acceleration down the slope, a=gsinx
Hence g = a/sinx. Now just sub the given value of acceleration and the angle x to find g