Option A:
Value of the $50 notes = 7 x $50 = $350
Amount left = $700 - $350 = $350
Number of $20 = . $350 ÷ 20 = 17.5 (Not a possible answer)
Option B:
Value of the $50 notes = 8 x $50 = $400
Amount left = $700 - $400 = $300
Number of $20 = . $300 ÷ 20 = 15 (Possible answer)
Option C:
Value of the $50 notes = 9 x $50 = $450
Amount left = $700 - $450 = $250
Number of $20 = . $250 ÷ 20 = 12.5 (Not a possible answer)
Option D:
Value of the $50 notes = 11 x $50 = $550
Amount left = $700 - $550 = $150
Number of $20 = . $150 ÷ 20 = 7.5 (Not a possible answer)
Answer B