Basic Peds Calculations HELP!!

New to Peds! Can anyone tell me if I am doing these calculations correctly??

1.

Order: Gravol 50mg IV q4h

Pt 11years, 40 kg

Recommended: 5mg/kg/day q6h

5mg x 40mg = 200mg divided by 6 doses (q4h) = 33.3 mg/dose

Therefore dose is incorrect and should be should be q6h though, therefore 200mg divided by 4 = 50mg/dose

2.

order: ancef 250mg IV q6h

Pt 4 years, 20kg

recommended: 100-150mg/kg/day q8h

20kg x 100mg /24h= 2000mg/3 doses = 666mg/dose

20kg x 10 mg/24h=3000 mg/3 doses = 1000mg/dose

therefore dose not appropriate, should be 666mg-1000mg/dose ?? Recommended says q8h and order says q6h so how do I solve that???

3. fluid maintenance for child who weighs 17kg:

a) Calculate 100% fluid maintenance = 54mls/hr

b) 120% for the next 12 hours and the rate??

THANK YOU!