What is the answer to negative 3square root6 plus 8square root of6?

Answer 1

-3√6 + 8√6 = ?

Assuming that's what you meant then:

-3√6 + 8√6 = (-3 + 8)√6 = 5√6

5√6 = √25√6 = √150 = 12.2474487 (approx 12.25)