Hello, I am trying to develop a bit of code for my assignment. this is my first time using JavaScript and I have most of my code correct but I am missing something. Here is my code so far:

<HTML>
<HEAD>
<TITLE>Gas Usage</TITLE>
<SCRIPT LANGUAGE = JavaScript>
var customerId = prompt ("Enter the customers ID number", -1)
var gasUsage = prompt ("Enter customers gas usage", 0)
var totalCustomers = 0
var totalAmountOwing = 0
while(customerId != -1) {
if (gasUsage <= 60) {
amountOwing = gasUsage * 2
}
else if (gasUsage > 60) {
amountOwing = (gasUsage - 60) * 1.5 + 105
}
document.write("Customer ID: " + customerId)
document.write(amountOwing)
document.write("<br/>")
customerId = prompt("Enter a Customer ID number", -1)
}
</SCRIPT>
</HEAD>
<BODY>
</BODY>
</HTML>

This is what I'm trying to display on the web page:

Customer ID: 1 has gas usage of 80 and owes $135
Customer ID: 2 has gas usage of 45 and owes $90
Customer ID: 3 has gas usage of 90 and owes $150
Customer ID: 4 has gas usage of 34 and owes $68
Customer ID: 5 has gas usage of 60 and owes $120
Customer ID: 6 has gas usage of 120 and owes $195
Total amount of customers is 6
Total amount for all customers is $758

This is the outcome when I run the code that I have:
1. It prompts to enter the customer id
2. It prompts for the gas usage
3. It prompts for the second customer id
4. It continues to prompt for the customer id until I enter -1
5. Depending on how many time I enter a value that isn't -1, it displays something like this:
Customer ID: 1135
Customer ID: 2135

So it's not prompting for the gas usage after the first gas usage prompt and just keeps displaying the first calculation next to each customer id I enter.

Could somebody please tell me what I'm doing wrong?

Thanks,
Matthew Quan