At first,

Brenda -> 11u

Diana -> 7u

Together, they have 18u.

In the end, Brenda had ½ of what Diana had.

18u ÷ 3 = 6u

Brenda -> 6u

Diana -> 12u

Celine -> no change at 5u

(a) B : C : D = 6 : 5 : 12

Brenda gave Diana (11u – 6u) = 5u candies

5u = 240

1u = 48

Total -> 11u + 5u + 7u = 23u 

(b) There were (23 × 48) = 1104 candies