Solve the circled question

The objective function for the problem is p1 (1000-100p) + p2*100(p1-p2) and to solve you use the two FOCs (first order conditions) jointly, i.e., solving p1 and p2 from two equations jointly.

Example - A retailer is selling a product to a population of 1000 potential customers - Customers' WTP to the product is uniformly distributed between $0 and $10 - Unit variable cost is 0 - What is the optimal single price? If the retailer can set two different prices in sequence, what are the optimal prices