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16x² - 49

Explanation:
To answer this question, we will multiply each term from the first bracket by each term from the second bracket and then combine like terms to get the final expression.

This can be done as follows:
(4x - 7)(4x + 7)
4x(4x) + 4x(7) - 7(4x) - 7(7)
16x² + 28x - 28x - 49
16x² - 49

Another easier way to solve this is to note that the given brackets can be solved using the difference between two squares. 
The rule can be stated as follows:
(a + b)(a - b) = a² - b²

Comparing this to the given brackets, we will find that:
(4x + 7)(4x - 7) = (4x)² - (7)² = 16x² - 49

Hope this helps :)