The question asks what stick force per g is required to move it from SLF. Working on this premise it assumes that the starting point is 280N/g, so is looking for how much more is needed.

 

The limit load factor is 2.5g, so the difference between 2.5 and 1.0g = 1.5g.

Additional stick force = 280 x 1.5 = 420N