Hey there! I'm happy to help!
The perimeter is the distance around the rectangle. You have used the word height, but I will replace it with the word width because the word height is usually used with 3D shapes.
If W is the width and the length is L, the formula for the perimeter is 2W+2L=P.
We can plug in the numbers we already have to solve for L, the length of our base.
2(14.2)+2L=66
28.4+2L=66
We subtract 28.4 from both sides.
2L=37.6
We divide both sides by 2.
L=18.8
The length of the base is 18.8 meters.
Have a wonderful day!