Its simple!
First, you turn -3.9 into a fraction
-3.9=

Now u solve

(1) Convert mixed numbers into fractions (im sure you know how to do this)

(2) Multiply across on both the denominator and numerator (bottom and top rows)

(Remember, negative ×/÷ positive is always negative)
(3) Make ur answer into an even fraction

I hope this helped! Srry I'm not that good in english