in a bank; on a bench
Minha irmã é secretária num banco.
My sister is a secretary at a bank.
Se foi acabar num banco, por que ele fez engenharia?
If he ended up in a bank, why did he study engineering?
— 3 Idiotas (2009)
He was sitting on a bench.
Tom estava sentando num banco comendo algo que parecia uma maçã.
Tom was sitting on a bench eating something that looked like an apple.
I used to work at a bank.
He works at a bank.
Seu filho não trabalha num banco.
Your son doesn't work at a bank.