Robert needs his daily fix of coffee in the mid-afternoon and visits different coffee shops that will give him as much utility as possible, given his $20/month food budget. On Monday, the Blue Coffee Shop was selling espresso shots for $3 each and Robert added 3 shots to his cappuccino. By Friday, the Purple Coffee Shop offered espresso shots for $2 each, while all other prices remained the same, so Robert was bold and added 4 espresso shots to his hot beverage.

Required:
Given this information, plot Robert's demand curve for espresso shots.