Refactoring game - how many changes would you make?

printBill.js

import {readFileSync} from "fs";
const plays = JSON.parse(readFileSync("../shared/plays.json"));
const invoices = JSON.parse(readFileSync("../shared/invoices.json"));

function statement(invoice, plays) {e
    let totalAmount = 0;
    let volumeCredits = 0;
    let result = `Statement for ${
        invoice.customer
    }\n`;
    const format = new Intl.NumberFormat("en-US", {
        style: "currency",
        currency: "USD",
        minimumFractionDigits: 2
    }).format;
    for (let perf of invoice.performances) {
        const play = plays[perf.playID];
        let thisAmount = 0;

        switch (play.type) {
            case "tragedy": thisAmount = 40000;
                if (perf.audience > 30) {
                    thisAmount += 1000 * (perf.audience - 30);
                }
                break;
            case "comedy": thisAmount = 30000;
                if (perf.audience > 20) {
                    thisAmount += 10000 + 500 * (perf.audience - 20);
                }
                thisAmount += 300 * perf.audience;
                break;
            default:
                throw new Error(`unknown type: ${
                    play.type
                }`);
        }

        // add volume credits
        volumeCredits += Math.max(perf.audience - 30, 0);
        // add extra credit for every ten comedy attendees
        if ("comedy" === play.type) 
            volumeCredits += Math.floor(perf.audience / 5);
        


        // print line for this order
        result += `  ${
            play.name
        }: ${
            format(thisAmount / 100)
        } (${
            perf.audience
        } seats)\n`;
        totalAmount += thisAmount;
    }
    result += `Amount owed is ${
        format(totalAmount / 100)
    }\n`;
    result += `You earned ${volumeCredits} credits\n`;
    return result;
}

console.log(statement(invoices, plays));