Answer:
Current SMA balance is $15,000
Step-by-step explanation:
SMA means special memorandum account, where excess margin recouped from investing the fund in customer's margin account is held.
Since ABC was bought for $10,000, while it's current worth is $20,000
Margin recorded = $20,000 - $10,000
 = $10,000
XYZ stock sells short at $10,000, while it's current worth is $5,000
Margin recorded on short sell 
 =$10,000 - $5,000
 =$5,000
SMA current balance 
 = $10,000 + $5,000
 = $15,000