Calculate the Area of an Isosceles Trapezoid with Height 3 and Side Length 4

For the trapezoid, we recognize that to calculate the area, we typically need both base lengths and the height. The area formula for a trapezoid is $A = \frac{1}{2} \times (b_1 + b_2) \times h$, but we lack the values of the bases $b_1$ and $b_2$. Thus, with given only the leg lengths as 4 units and height as 3 units, and without base lengths, calculation of area is impossible.

Therefore, the solution is that it is not possible to calculate the area with the provided information.