Nora took 10 bottles of water to a picnic. Of these bottles of water, she and her friends opened a certain number of bottles, b. What expression can be used to determine the number of unopened bottles at the end of the picnic?

10 - B = U

Step-by-step explanation:

U stands for the unopened bottles

for example if they opened 3 bottles it would be 10 - 3 = U (unopened bottles)

The value of U is 7 because the 10 bottles of water minus the 3 bottles they opened it would equal 7.

therefore the equation 10 - B = U shows the amount of unopened bottles

the answer is 21%.