Let Joy be x years old
Joy's brother's age is 3 years older than twice joy's age.
Joy's Brother = 2x + 3
The sum of Joy's age and her brother's age is 24.
x + 2x + 3 = 24
3x + 3 = 24
3x = 24 - 3
3x = 21
x = 21 ÷ 3
x = 7
Joy:
x = 7
Brother:
2x + 3 = 2(7) + 3 = 17
Difference in their age = 17 - 7 = 10 years
They are 10 years apart.