Answer:
Let M be the age of Maggie and B the age of her younger Brother:
Rewrite the problem from English language to Math's:
B = 2.M - 10 (1)
and M + B = 29 (Given) OR B = 29 -M (2)
Plug 2) into 1):
29 -M = 2.M -10
29 + 10 = 3 M →→3M = 39 and M = 39/3 = 13
Replace M by 13 and you will find B =6
Then Maggie = 13 year old and her brother B = 6 year old