Let x be the Maggie's age and y be her brother's age.
Then you have two equations:
1. y = 2x -3, and
2. x + y = 24.
So, you need to solve the system of two linear equations in two unknowns
{ y=2x-3 and x+y= 24
Express y from the second equation y = 24 - x and substitute it into the first equation. You will get 24 - x = 2x - 3.
Simplify it step by step:
24 + 3 = 2x + x,
27 = 3x,
x = 27/3 = 9.
Answer: Maggie is 9 years old
Hope this helps!