These questions join the support tickets to customers and employees, and the buying tables suppliers, product_suppliers and purchase_orders to products.
Before each query, decide two things. What should one row of the answer be (a ticket, a customer, a supplier)? And should rows with no match stay, which means a LEFT JOIN? Some tickets have no agent yet, one supplier supplies nothing, and many customers never opened a ticket.
Count with a column from the right-hand table when a LEFT JOIN can leave it empty, and use COALESCE where the task asks for a value instead of NULL.