63 and 45 are both divisible by 9.
63:45 = 7:5
63 blue balloons to 45 red balloons is the same ratio as 7 blue balloons to 5 red balloons.
Since now you want the number of red balloons to be 10, then
7:5 = x:10
x = 14
Answer: A group that has 10 red balloons has 14 blue balloons.