a.€300
1) If give up now - lose €1000
2) If complete the stand with another €300,you'll lose only €500+cost of running the hotdog stand (€1000+€300 - €800).If you can increase the sales,the lost will be less but it may cost for advertising.So,stick to the €300 extra cost and hope for the best.Worst case:No sales,lose $1300 plus cost of running the stand (like buying the hotdog and employing someone...)
Fun of running a business!