The correct answer is D. This is calculated by firstly computing the trend for fourth quarter of 2015 (Y = 4,000 + 6 x 8 = 4,048) and then adding a seasonal adjustment of 5, to give forecast sales of 4,053.
The most popular choice was alternative C. This indicates that many candidates were able to calculate the trend but failed to apply the seasonal adjustment. Distracters (the incorrect answers to objective test questions) are often based upon partially complete calculations. Candidates are advised not to stop thinking as soon as they generate a number that corresponds with one of the options offered. A good way of avoiding this trap is not to look at the answers until you are satisfied that you have fully completed your calculation.
Answer A used a value of 4 for period 4 of 2015 and generated the wrong trend figure, but then correctly processed the seasonal adjustment.
Finally a minority of candidates selected answer B, indicating that they could correctly calculate trend but subtracted rather than added the seasonal adjustment.