Answer:
0%
Step-by-step explanation:
It was a little hard to see your cross, so I made another one and it is attached below.
So what you are looking for is the likelihood of an offspring with a phenotype of brown spots and short tails.
Without using the Punnet, we can already deduce that it is 0%. This is because brown spots are recessive, and the only way a brown spotted dog would have this trait, is each parent had at least 1 recessive allele for this trait.
So the expected genotype for brown spot would be:
bb
Only one of them has this, so they cannot have brown spots.