To find the unit rate, you just need to divide the total cost of the amount of items purchased by the amount of items purchased.
If 7 balloons costs $9.10, then you just need to divide 9.1 by 7 to get the unit price.
9.1 / 7 = 1.3
If 7 balloons costs $9.10, then one balloon costs $1.30.
The unit rate for the balloons is $1.30.
Hope that helped =)