A/an is the result of medical treatment that yields the exact opposite of normally expected results.

The answer to this question is the term adverse. Adverse term in treatment means an unsuitable or opposite result that a patient receives after a treatment. Adverse effect in medicine also shows a harmful or negative effect from drinking the medicine. Adverse effect is also known as a side effect.

n = 6.39

Explanation:

2.3 + 4.09 = n
6.39 = n

Swap the sides of the equation
n = 6.39