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.

b.my answer is b.

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