Note that 13 3/4 = 13.75.
The cost of purchasing the stock is
(50 shares)*(13.75 $/share) = $687.50
The revenue generated by selling the 50 shares at $12 per share is
(50 shares)*(12 $/share) = $600.00
Gain = 600.00 - 687.50 = - $87.50
The loss is $87.50
Answer: $87.50