First question
①Brenda has ½ more sweets than Faith.
½ is 1 out of 2.
So we can say that Faith has 2 units of sweets and Brenda has 1 unit more than her. Brenda has 3 units.
Ratio of sweets of Brenda to Faith = 3 : 2

②Faith has 3/7 less sweets than Vivian.
3/7 is 3 out of 7.
So we can say that Vivian has 7 units of sweets and Faith has 3 units less than her. Faith has 4 units.
Ratio of sweets of Faith to Vivian = 4 : 7

Now we have a repeated identity, Faith. We should make her units the same number for both ratios, since it's for the same person.
We can change 3 : 2 into 6 : 4
Ratio of sweets of Brenda to Faith = 6 : 4
Now we can write the ratio comparing all three girls.

Ratio of sweets of Brenda to Faith to Vivian = 6 : 4 : 7
Total number of units = 6+4+7=17
So 17 units = 289 sweets
1 unit = 289 sweets ÷ 17 = 17 sweets

Number of sweets Vivian has = 7 units
= 7 x 17
= 119