Maggie's brother is 5 years younger than twice her age. the sum of their ages is 28. how old is maggie?

you in advance ; 3;

Let us denote Maggie's years (her age) with M and her brother's with B.
We know that: 
Maggie's brother is 5 years younger than twice her age. So, we can write the equation:
B=2*M-5 (1)
We also know that the sum of their ages is 28, so we can write:
M+B=28 (2)
M=28-B (3)

Let put in equation (3) equation (1):
M=28-(2M-5)
M=28-2M+5
3M=33
M=11 Maggie is 11 years old.
B=28-11=17 Her brother is 17 years old.