Answer:
$18,480
Step-by-step explanation:
Cost of van = $51,000
Useful life = 5 years
Salvage value = $4,800
Using the straight line, Annual depreciation 
= (51000 - 4800)/5
= $9,240
Using the Double-declining balance method,
Annual depreciation = 2 × 9,240
 = $18,480