The right question is that the lowest altitute is 3^8 feet
You are told that the highest altitude is 3 times the lowest altitude =>
highest altitude = 3 * lowest altitude = 3 * 3^8 feet.
Now you use the ruel of mutiplication of powers with the same base: copy the base and sum the exponents => 3 * 3^8 = 3 ^(1+8) = 3^9.
Note: remember that 3 = 3^1.
Answer: 3^9 feet