Direct and Inverse Proportions

Which of the following mathematical statements correctly represents the condition for two quantities $x$ and $y$ to be in direct proportion (where $k$ is a constant)?

If the cost of $15$ kg of sugar is ₹$600$, what is the cost of $8$ kg of sugar?

On a map, a scale of $1$ cm represents $50$ km. If the distance between two cities on the map is $4.5$ cm, what is the actual distance between them?

If $6$ men can construct a shed in $4$ days, how many days will it take $8$ men to construct the same shed?

$40$ men can finish a job in $26$ days. How many men are required to finish the same job in $20$ days?

$12$ pipes can fill a tank in $2$ hours. How long will it take $3$ pipes to fill the same tank?

If $10$ oranges cost ₹$80$, what is the cost of $1$ dozen oranges?

If $14$ men can dig a trench in $6$ days, how many men can dig it in $4$ days?

In a model of a ship, the mast is $9$ cm high, while the mast of the actual ship is $12$ m high. If the length of the ship is $28$ m, how long is the model ship?