The polynomial expression represents the area of the trapezoid is:

Solution:
Given that,
The bases of an isosceles trapezoid are represented by 3x and (3x + 4)
The height of the trapezoid is represented by (x + 2)
To find: area of the trapezoid
The area of the trapezoid is given as:

Where b₁ and b₂ are the bases and h is the height
Therefore,

Thus the polynomial expression represents the area of the trapezoid is found