Each of the terms here (64, a^3, b^15, c^6) have a cube root.
The cube root of 64 is 4, the cube root of a^3 is a, the cube root of b^15 is b^5, and the cube root of c^6 is c^2.
You end up with the square root of 4 times a times b^5 times c^2
√4ab⁵c²