Question 389559
I will assume the given exponent of 3 in the front part of the radical is the index.  In other words the problem is to find the cube root of -64 which is -4

note: roots of negative numbers of odd indices (3,5,7, etc) are negative real numbers
roots of negative numbers of even indices (2,4,6, etc) are not valid real numbers, and the roots are called imaginary