I would use a growth strategy framework concentrating on the usage of marketing only. Since the question is explicitly on marketing, I would assume it is not feasible to consider new products. Thus, a possible structure could be the following:
1) Clarify the goal and client information.
This will mainly include the analysis of:
- The specific goal of the client
- The potential constraints involved.
2) Identify the segment with the highest growth potential.
This will involve the following:
- Analysis all the segments our client is present
- Benchmark of competitors to understand which one has the highest potential in terms of growth and size.
Since in this case you had a sales drop, it is likely the key segment will be the one where the drop took place.
3) Identify the best growth strategy.
A good growth strategy will include the analysis of the variable to target and the way to apply such strategy. Assuming that for sales the question meant revenues and not sales volume you could structure as follows (if they meant sales volume, just cut the price bucket):
- Strategy to increase revenues
- Increase price (eg better marketing of prices to different segments to generate price discrimination)
- Increase volume (eg promote discounts)
- Way to apply the strategy
- Online marketing channels (eg online ads)
- Offline marketing channels (eg marketing in retail shops)
4) Shortlist top strategies and double check if you have all the capabilities.
Once defined the optimal segment, whether to target a price or volume increase and the best channel, you should end with a list of the most valuable strategies. You should now rank them in terms of:
- Expected results in terms of your goal
- Capabilities required, which should match your constraints
You can then choose the one that has the highest expected result and matches the constraints verified in step 1.
5) Consider risks of the strategy.
As a final step, you can check which are the risks involved with the strategy chosen – for example, whether there is any risk of a competitor reaction or longer timeline to hire the required stuff to implement the new action.