Answer:
$1300
Step-by-step explanation:
Initial amount of loss (lesser of AB or decline in value less insurance proceeds): 
Asset A: $7000 - $2000 = $5000 
Asset B: $4000 - $4000 = $0
Asset C: $1700 - $900 = $800 
Total = $5800 
10% of AGI = $4,200 
Therefore, Wally's casualty loss deduction is: $5800 - $300 - $4200 = $1300