jmc

Writing everything in terms of prime factorizations, the given expression is $\sqrt{3\cdot 5^2\cdot 2\cdot 2\cdot 7\cdot x^3}=\sqrt{(2^2\cdot 5^2\cdot x^2)\cdot (3\cdot 7\cdot x)}=\boxed{10x\sqrt{21x}}$.