Volume of the candle:
V = B * h ( where B is the base area and h is the height )
270 = B * 18
B = 270 : 18
B = 15 cm²
B = a * b / 2
B = 5 * b / 2
15 = 2.5 b
b = 15 : 2.5
b = 6 cm
Therefore dimensions of the box are: a = 7cm, b = 6 cm, c = 18 cm.
Answer: B ) 7 by 6 by 18 cm.