Barbara's sister is twice as old as Barbara. Barbara's sister is 7 years younger than Barbara's brother. If Barbara's brother is 21, which equation could be used to find Barbara's age (b)?

Option D

Step-by-step explanation:

Let the age of Barbara sister = x years

And the age of Barbara's brother = y years

"Barbara's sister is 7 years younger than Barbara's brother"

x = y - 7

If y = 21,

x = 21 - 7 (1)

"Barbara's sister is twice old as Barbara"

x = 2b (2)

By substituting the value of x from equation (2) to equation (1),

2b = 21 - 7

2b + 7 = 21 + 7

2b + 7 = 21

Therefore, Option D will be the answer.

it's both, now can you answer my most recent question?

mr. flanders’ class sold 47 doughnuts and   mr. rodriquez’s class sold 38 cartons of milk

step-by-step explanation:

let x be the number of doughnuts sold by mr. flanders’ class and y be the number of cartons sold by mr. rodriquez’s class.

1. together, the classes sold 85 items, then

x+y=85.

2. both classes earn earned $104.49 for their school. if doughnuts were sold for $1.35 each, then x doughnuts costed $1.35x. if cartons of milk were sold for $1.08 each, then y cartons costed $1.08y. hence,

1.35x+1.08y=104.49.

3. solve the system of two equations: