The child weighs is 16 kg and the usual pediatric dose is 30 to 50 mg/kg/24 h. Then the daily dose would be: 30-50 mg/kg/24 h. * 16kg= 480-800 mg /24hr.
Erythromycin suspension is given q6h, so you need to divide it by 4, then dose per administration would be: 480-800 mg /24hr / (4times/24hr)= 120-200/times