Answer:
3 black gebrils have straight tails
Explanation:
Given - 
First group of true breeding gebrils have black fur and curly tails
Second group of true breeding gebrils have yellow fur and straight tails
After the F1 generation, all the offspring would have black fur and curly tail
This means black fur is dominant over yellow fur and curly tail is dominant over straight tails
Let "Black fur" be represented by "B" and "yellow fur" be represented by "b"
Let curly tail be represented by "C" and straight tail be represented by "c"
Then parents genotype for F1 generation would be "BBCC" and "bbcc"
and genotype of first generation offspring would be "BbCc"
BbCc
 BC         Bc         bC        bc
BC	BBCC	BBCc	BbCC	BbCc
Bc	BBCc	BBcc	BbCc	Bbcc
bC	BbCC	BbCc	bbCC	bbCc
bc	BbCc	Bbcc	bbCc	bbcc
Black Curly – BBCC, BBCc, BbCC, BbCc, BBCc, BbCc, BbCC, BbCc, Bbcc,  
Yellow curly- bbCC, bbCc, bbCc
Black straight – BBcc, Bbcc, Bbcc
Yellow straight- bbcc
3 black gebrils have straight tails