You can solve for the base by inputting all the values you know into the volume formula for a triangular pyramid, which is:
(1/3)bh = V
where b = base and h = height.
(1/3)b(6) = 128
2b = 128
b = 64 feet.
hope that helps!! if you liked this answer please rate it as brainliest so I can gain the next rank!! thank you!!!!