SOLID Principles and Code Smells

You're a Consultant at MATRIX Resources reviewing a client's invoicing service before recommending a refactor. Look at this class and identify which SOLID principles it violates.

class MySQLDatabase {
    void save(String table, long id, double value) {
        // writes directly to a MySQL connection
    }
}

interface InvoiceService {
    double process(Invoice invoice);
    void refund(Invoice invoice);
    void generateTaxReport(Invoice invoice);
}

class InvoiceProcessor implements InvoiceService {
    private MySQLDatabase db = new MySQLDatabase();
    private EmailClient emailClient = new EmailClient();
    private PdfRenderer pdfRenderer = new PdfRenderer();

    public double process(Invoice invoice) {
        double total = 0;
        if (invoice.getType() == "STANDARD") {
            total = invoice.getSubtotal() * 1.08;
        } else if (invoice.getType() == "CONTRACTOR") {
            total = invoice.getSubtotal() * 1.08 + 15.0;
        } else if (invoice.getType() == "NONPROFIT") {
            total = invoice.getSubtotal();
        }

        db.save("invoices", invoice.getId(), total);
        emailClient.send(invoice.getClientEmail(), "Your invoice total is " + total);
        pdfRenderer.render(invoice, total);

        return total;
    }

    public void refund(Invoice invoice) { /* ... */ }
    public void generateTaxReport(Invoice invoice) { /* ... */ }
}

class DiscountedInvoiceProcessor extends InvoiceProcessor {
    @Override
    public double process(Invoice invoice) {
        throw new UnsupportedOperationException("Discounted invoices use a different pipeline");
    }
}

Name each SOLID principle this violates, point to the exact line or method responsible, and explain the consequence in plain terms as if you were advising the client.