We can simplify the expression on the left side of the equation as $4 \cdot 2^x = 128$.
Dividing both sides by 4 gives $2^x = 32$.
Taking the logarithm base 2 of both sides gives $x = 5$.
Therefore, $(x + 1)(x - 1) = (5+1)(5-1) = \boxed{24}$. 
The answer is: 24
Below is a math problem. Provide a detailed, step-by-step solution.

### Problem:
Given that $2^x+ 2^x+ 2^x+ 2^x= 128$, what is the value of $(x + 1)(x - 1)$?

### Answer:
