Amanda is 3 years older than Brantley and Carlos is twice as old as Amanda. The sum of their ages is 57. How old is Amanda?

15

Step-by-step explanation:

A = B + 3

B = A - 3

C = 2A

A + B + C = 57

A + A - 3 + 2A = 57

4A - 3 = 57

4A = 60

A = 15

15 years old

Step-by-step explanation:

Let's say Amanda's age is a, Brantley's age is b, and Carlos's age is c.

"Amanda is 3 years older than Brantley" means that a = 3 + b

"Carlos is twice as old as Amanda" means that c = 2 * a = 2a

"The sum of their ages is 57" means a + b + c = 57

We know that a = 3 + b, which can be written as b = a - 3. Substitute a - 3 in for b and 2a in for c in the equation a + b + c = 57 so that we have one variable to solve for:

a + b + c = 57

a + (a - 3) + 2a = 57

4a - 3 = 57

4a = 60

a = 15

Amanda is 15 years old.