Answer:
Height is 18 inches.
Base is 36 inches.
Explanation:
Let the base of the triangular table top be x inches.
The height will be 
x inches.
The area of the triangular table top is 324 inches²
Area of a triangle = 
 × Base × Height
342 inches² = 
 × x × 
x
 = 324
Finding the square root on both sides gives;
 = 18
Therefore x (the base) = 36 inches
And 
 (the height) = 18 inches.