how do u factor these polynomials~

Question

5x^2 - 5x-60

81-x^4

18a^2b-50b

Answer 1

(5x-20)(x+3)

-(x^2-9)(x^2+9)

Then are you sure the third one is written right? 18a^2b- is a to the 2b or is b something else

Answer 2

its A squared b