8ft is the length of the rope on the outside of the tent. I hope its right!
Kite Area = (Diagonal 1 * Diagonal 2) / 2
Diagonal 2 = 2 * Kite Area / Diagonal 1
Diagonal 2 =2 * 60 / 15
Diagonal 2 = 120 / 15
Height = 8 inches
The answer to your question is A.