Six lords came to live in the city of Gimiro. The first lord built himself a tower. The second lord built a tower that was 6 feet higher than the first lord's tower. The third lord built a tower 6 feet taller than the second lord's tower. Each lord built a tower 6 feet taller than the tower built by the lord before him. The sixth lord's tower was 40 feet high. If the six towers were piled on top of each other, how high would they reach?