A player is riding a boat down the river at a constant speed

Suppose the tourist can walk a kilometer. According to the question, a/(18+3)+a/(18-3)≤(meaning less than or equal to) 4 a/21+a/15 ≤4 5a+7a≤420 a≤35 Answer: Tourists can travel up to 35 kilometers. Or: Assume that the furthest the tourist can travel is A kilometers. According to the question, A/(18+3)+A/(18-3)=4 A/21+A/15=4 5A+7A=420 A=35 Answer: Tourists can travel up to 35 kilometers.