The height of trapezoid is 18 yards
Solution:
Given that, trapezoid has an area of 342 square yards
The length of one base is 17 yards, and the length of the other base is 21 yards
To find: height of trapezoid
The area of trapezoid is given by formula:

Where "h" is the height
"a" and "b" are the length of base
Here given that,
area = 342 square yards
a = 17 yards
b = 21 yards
h = ?
Substituting the values we get,

Thus height of trapezoid is 18 yards