We have,
x2+y2+2x+4y−4=0
⇒x2+2x+1+y2+4y+4=9
⇒(x+1)2+(y+2)2=32
Centre≡(−1,−2)

CP=(−4+1)2+(1+2)2=32
Centre of smallest circle is A
Centre of largest circle is B.
r2=∣CP−CA∣=32−3
r1=CP+CB=32+3
Hence,
r2r1=32−332+3=9(32+3)2
⇒r2r1=(2+1)2=3+22
Hence,
a=3,b=2
a+b=5