Given the stream of consciousness rationale, provide a reasonable question and answer. Rationale: In 7 weeks 5 * 7 = 35 goldfish die. In 7 weeks, Martin purchases 3 * 7 = 21 goldfish. In 7 weeks, Martin will have 18 - 35 + 21 = 4 goldfish.
 The question and answer:
Martin has 18 goldfish. Each week 5 goldfish die. Martin purchases 3 new goldfish every week. How many goldfish will Martin have in 7 weeks?
The answer is 4