To do this one you need to extract TIME and DISTANCE from the graph on page 3 of the SEP section:

Given OAT +5, FL75 ...... 9 minutes 18 NAM

Now, there is a 20kt HEADWIND .... if you are in a 20 kt wind for 9 minutes, you get 'blown':

20 x (9/60) = 3 nm ..... its a headwind, so -3nm .... 18 - 3 = 15 NGM

Additional assistance….

A NAM (Nautical Air Mile) distance is a Still Air distance (nil wind), a Nautical Ground Mile (NGM) distance is the distance you cover over the ground ....

Suppose your climb takes 50 NAM and 1 hour exactly .... in still air conditions (nil wind) you will travel 50NGM. If the mean wind component is '20kts HEAD WIND', the 'air' you are climbing in is moving backwards over the ground at 20kts - in other words, you will travel (50-20)=30NGM.

If your climb takes 50 NAM and 30 minutes .... if the mean wind component is '20kts HEAD WIND', the 'air' you are climbing in is moving backwards over the ground at 20kts - you are in this 20 kt wind for ½ hour .... you will get blown 10nms - in other words, you will travel (50-10)=40NGM.