Exercice : table with wrong markup

What is wrong with this table and how would you correct the markup?

reimbursements
Cost Social security Dental Dental+
Orthodontic treatment 2395€ 720€ 1259€ 1689€
Traumatic accident 2889€ 0€ 350€ 1912€
Crown 663€ 0€ 175€ 541€
Implant + crown 2001€ 50€ 225€ 1066€