sum of costs from another table by current ID

I have 3 tables:

"Cars" table, where every car has an ID.

"Operations" table that holds the operations have been done on a car.

| ID  | CarID | Operation | User | JournalID |
| --- | ----- | --------- | ---- | --------- |

"Journal" table that records the costs of the operations and other daily expenses:

| ID  | Amount | Date |
| --- | ------ | ---- |

What I want is knowing the sum of operations costs amount of a specific car, I was looping through all operations of that car and then looping for every journal row to sum, which lead to a bad result of course.

What can I do in that case to get the result as fast as possible?

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