Final answer:
The remaining balance on the card after buying 50 prints is $17.50.
Step-by-step explanation:
The remaining balance on the gift card after buying x prints can be found using the equation B = 20.50 - 0.06x. To find the remaining balance when Kira bought 50 prints, substitute x with 50 in the equation. B = 20.50 - 0.06 * 50 = 20.50 - 3 = $17.50.