Answer
If Tex withdrew from the market, the market demand curve curve would shift leftward
If Dex doubled his purchases, the market demand curve would shift rightward
Work Step by Step
If Tex withdrew from the market, market demand would decrease, and hence at each price the quantity demanded would decrease, and the demand curve would shift leftward
If Dex doubled his purchases, market demand would increase, and hence at each price the quantity demanded would increase, and the demand curve would shift rightward
