hope this helps! :)
x = amount invested @ 8% (24000 - x) = amount invested @ 7.2% (.08)*x = 2/3(.072)(24000 - x) 3*(.08x) = 2*(.072)(24000 - x) .24x = .144(24000 - x) .24x = 3456 - .144x .384x = 3456 x = 9000 (24000 - x) = 15000 check (.08)*9000 = 2/3(.072)(24000 - 9000) 720 = 2/3(.072)(15000) 720 = (.144)(5000) 720 = 720