$4.$ In the building where I work, every office has a phone, and every phone has a unique number. If you know a person's phone number, you can call them. For example, my phone number is $53.$ However, today, my office is being painted, so I$\text{'}$m going to work in Vivian's office. Her phone number is $97.$ I$\text{'}$m going to forward my phone number to hers, so that if anyone calls me on my phone number, it will ring in her office $($where I will be$).$ Meanwhile, her phone number will continue to work as usual. We can represent the situation using a dict:

forwards $=\{53$: $97\}$

The forwards dictionary stores all of the current numbers that are being forwarded. The key shows that number that is being forwarded, and the value shows the number that it is being forwarded to$.$ However, it turns out that Vivian's office is also being painted today, so we're both going to work in Bob's office, who has phone number $24.$ If we forward Vivian's phone number to Bob's, we ensure that both I and Vivian can get calls in Bob's office. Our updated forwards dictionary looks like this:

forwards $=\{53$: $97,97$: $24\}$