-7√5
rewrite 20 as 2^2·5
factor 4 out of 20. negative ∛4(5)-√5
rewrite 4 and 2^2 negative ∛2^2·5-√5
pull terms out from under the radical
-3(2√5)√5
multiply 2 by -3
-6√5-√5
subtract √5 from -6√5
the answer is -7√5
