To solve the exponential equation \( 4^{3x} = 64 \), we start by expressing 64 as a power of 4.
Notice that: \[ 64 = 4^3 \]
This allows us to rewrite the equation: \[ 4^{3x} = 4^3 \]
Since the bases are the same, we can set the exponents equal to each other: \[ 3x = 3 \]
Now, divide both sides by 3: \[ x = 1 \]
Thus, the solution to the equation \( 4^{3x} = 64 \) is: \[ x = 1 \]
So, the correct response is \( x = 1 \).