There are two problems that i just am not sure about can someone please help me. It says

Find tthe follow for f(X)=x^4-8x^2+15

Approximate all the real zeros to the nearest hundredth

also i have one more

find the following for f(X)= x^3+3x^2+9x+27

A. The number of zeros

B all zeros exactly

C. Factor f(X)