A parallelogram is a quadrilateral with 2 pairs of parallel sides. This means opposites sides are parallel to each other. Opposite angles and sides are congruent.
From your question the base of the parallelogram is given as 12 units and the sides is 10 units. The area of the parallelogram is given as 140 units². What is left is the height of the parallelogram.
Using the formula for finding the area of a parallelogram, the height can be found.