Answer: 
Step-by-step explanation:
A line that cuts a circle at two points is called "secant".
There is a theorem known as "Intersecting Secant Theorem". This is the theorem you need to use to find the value of "d".
According the Intersecting Secant Theorem:

Having this expression, the next step is to solve for "d":
Use Distributive property:

Subtract 256 from both sides:


Divide both sides by 16:

The value of "d" rounded to the nearest tenth is:

Answer:
Step-by-step explanation:
All you do is divide
For a, what is 10 divided by 2? The answer is 5!
For b, what is 21 divided by -3? The answer is -7!
For c, what is 6 divided by 1/3? The answer is 18!
For d, what is -7 divided by -1/2? The answer is 3.5!