When we square brackets, it is always advised to write out the brackets fully.
(7x - 6)² becomes
(7x - 6)(7x - 6)
Next, we follow FOIL
First (The first term in the set 1 multiplied by the first term in set 2)
Outer (The first term in set 1 multiplied by the second term in set 2)
Inner (The second term in set 1 multiplied by the first term in set 2)
Last (The second term in set 1 multiplied by the second term in set 2)
F 7x x 7x = 49x²
O 7x x -6 = -42x
I -6 x 7x = -42x
L -6 x -6 = 36
Now, we add together all the terms
49x² + -42x + -42x +36
Adding a negative is the same as subtracting
49x² - 42x - 42x + 36
Finally, simplify (add together the like terms)
49x² -84x + 36