X = the brother
c = carly
c = 3x
c + x < = 24
now we sub
3x + x < = 24
4x < = 24
x < = 24/4
x < = 6 ...oldest age the brother can be is 6
$640 in interest after 6 months
$8,640 is the balance after six months
Divide the price by amount to find out how much each costs. multiply that by 9. 4 (divided by) 8 = .5, or 50cents. each apple is 50cents. multiply .50 by 9. It costs 4.50. Hope this helps
11,15,19,23
an = 11 + 4(n-1)
an = 11 + 4n - 4
an = 4n + 7