I can't figure these out....

1)square root of 252x^14y^31

2) 3 square root of 10 times square root of 490

3) 7 cubed root of 40 (minus) cubed root of 625 (plus) 7 cubed root of 5.

4) for the square root of negative 25...is the answer 5i ?

any help would be awesome because I'm stuck