$1.$ Transactions:

January $1$: Invested $$100,000$ cash to start the business.

January $5$: Received $$20,000$ cash from a client for plumbing services to be provided.

January $10$: Paid $$4,000$ for office rent for the month.

January $15$: Purchased office supplies for $$1000.$

January $20$: Provided plumbing and heating services to clients on credit, totaling $$16,000.$

January $25$: Received $$10,000$ from clients for services provided earlier.

January $30$: Paid $$6,000$ for salaries to employees.

$3.$ Posting to the Ledger: