I am not quite sure what the question asks for,
But this is what i assume it wants:
Cos A= 0.6489
In this given one, we basically find the size of the angle A
we do cosine inverse on both sides to get the size of the angle A

: It looks like this in the calculator

× cos A=

(0.6489)
(

and cos cancels out)
A=

(0.6489)
A=49.54°
check:
cos 49.54=0.6489 (its right!)
Using the distributive property the product is -12x-20. To distribute you take the numbers and or variables outside of the paranthesis and multiply it by each one in the parenthesis such that 4x is multiplied by -3x getting -12x and multiplying 4x by -5 and the product is -20x and all together the answer is -12x-20
According to the information given in the exercise, the following expression represents the area of the rectangular garden:

And the following expression represents the combined area of the walkway around the rectangular garden and the area of the garden:

You can identify that the word "combined" indicates that that expression was obtained by adding both areas.
Knowing the above, you can set up the following equation:

Where "A" is the area of the walkway around the rectangular garden.
Solving for "A", you get the following expression:

The answer is:
16 square kilometers is 3953.6861 acres.