Answer:
17
Explanation:
Let x be the number of roses in the first yard. If in the first yard there are 10 roses less than in the second one, then in the second yard there are x+10 roses.
If 9 roses were transplanted from the second yard to the first one, then in the first yard the number of roses is x+9 and the number of roses in the second yard becomes x+10-9=x+1. After transplantation the first yard would have 2 times more roses than the second one, thus

There are x+10=7+10=17 roses in the second yard.