We can figure out the answer to this problem by studying the signs.
To get the “-” in 16x^2 – 36, we need a “+” and a “-” so when they are multiplied together they will equal a “-“.
Answer (1) has 2 negatives that when multiplied will equal a positive
Answer (3) has 2 negatives that when multiplied will equal a positive
Answer (4) has 2 positives that when multiplied will equal a positive
So find the one that has a positive and negative!  2 points 🙂