A litre of petrol costs US$150. What is the cost of x litres of petrol? (Write the expression in terms of x)

1. Break Down the Problem

To find the cost of $x$ litres of petrol, we need to establish the relationship between the cost of petrol and the volume purchased.

2. Relevant Concepts

The cost per litre of petrol is given as $US\$150$. Therefore, the total cost for $x$ litres can be expressed as:

$\text{Total Cost} = \text{Cost per litre} \times \text{Number of litres}$

3. Analysis and Detail

Substituting the values into the expression, we have:

$\text{Total Cost} = 150 \times x$

4. Verify and Summarize

This expression accurately represents the total cost for any volume $x$ litres of petrol, where $x$ can be any positive real number.

Final Answer

The cost of $x$ litres of petrol is given by the expression:

$150x \, (in \, USD)$