Refer to figure. 
The easiest and fastest way to solve this exercise is by drawing vectors: 
In both cases (forecast and actual wind), the wind comes from the right, causing a left drift. The wind vector will be the same length for both scenarios (= wind speed).

Start by drawing your aircraft and its True heading (040°). From this point, draw a vector representing the forecast wind of 100°. Draw a line which depicts the planned track by adding the vectors.

Now, draw a second vector, with the same length as the first one but this time with the approximate direction of the actual wind experienced (160°). Draw the actual track by adding the vectors.

As you can see in the attached figure, the forecasted wind 100°/40 kt will cause a greater left drift and, as a result, the actual track flown will be to the right of the planned.