Question

Matthew is 7 years older then twice the age of his sister. If Matthew is 13, how old is his sister?

Answer 1

Let:
The age of Mathew's sister be x
The age of Matthew will be 2x+7
=> 2x+7=13
=> 2x=13-7
=> 2x=6
=> x=6/2
=> x=3

Hope this helps!