Volume is the product of base area and height.
The first candle will have a volume of
.. V = Bh = (21 cm^2)*(8 cm) = 168 cm^3
The second candle will have a volume of
.. V = Bh = (7 cm^2)*(14 cm) = 98 cm^3
The total volume of the two candles is
.. 168 cm^3 +98 cm^3 = 266 cm^3
Josie is 6 cm^3 short of the amount required for the two candles she has in mind.
No, the base area of the second candle cannot be 7 cm^2. There is not enough wax to make a candle with that area 14 cm tall.