There's a 30 coefficient on the first and no coefficient (i.e. a 1) on the second. So the GCF of the constant part is GCF(30,1)=1.
Similarly, [tex]GCF(x^3, x^5)=x^3[/tex] because both have [tex]x^3[/tex] as a factor.
[tex]GCF(y^4,y^3)=y^3[/tex] because both have [tex]y^3[/tex] as a factor.
Now that we see how the bits work it's not too hard to read these off:
[tex]GCF(30x^3y^4, x^5y^3)=x^3y^3[/tex]
