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Question: In which year will China need to start importing metal from Colombia?

Requirement: Build a simple model to answer the above question

Assumptions China's demand is either met through domestic production or imports. The preference is listed below and based on price and existing relationship

1. Domestic

2. India

3. South Africa

In 2018 China consumed 20, 40 and 55 tons from these sources, respectively

The maximum outputs are 20, 45 and 75 tons for each of these sources, respectively

Chinese demand for metal is expected to increase at 5% p.a. going forward

Imports from India grow by a year-on-year maximum of the overall demand growth i.e., 5%

Any shortfall in supply is made up by the next country in order of preference. For example, if India reaches its maximum output, South Africa makes up the difference (if not at maximum output as well)