The area of a parallelogram is 392 m2.

Area of the parallelogram = 392 m2
Let the base of the parallelogram be b m.
Given:
Height of the parallelogram is twice the base.
∴ Height = 2b m

Area of a parallelogram $=$ Base $x$ Height

$\Rightarrow 392=b \times 2 b$

$\Rightarrow 392=2 b^{2}$

$\Rightarrow \frac{392}{2}=b^{2}$

$\Rightarrow 196=b^{2}$

$\Rightarrow b=14$

∴ Base = 14 m

Altitude $=2 \times$ Base $=2 \times 14=28 \mathrm{~m}$