Answer:
a promissory note
Explanation:
Based on the information provided within the question it can be said that the instrument that Ewa signed is most likely a promissory note. This is a not that enforces an unconditional promise, from one individual to another promising to make a certain payment in a certain time period. Which is exactly what EWA is signing when agreeing to pay $5,000 with interest in installments with the final payment due June 1, 2013.