Answer: 50.24
Area of a circle is pi times r^2
The r is 1/2 the d
So 8/2 = 4
Pi times 4^2= 50.24
The equation is put in slope intercept form which is y=mx+b
The slope is m and in this case it is -1/2.
To find the y intercept substitute in 0
for x then solve.

I think #4 is 4 but I'm not completely sure
Answer:
Jack is 8
Step-by-step explanation:
j= jacks age
2j+5 =21
This is the equation from Twice jacks age plus five is 21
We want to isolate j
Subtract 5 from each side
2j+5 =21
2j+5-5 = 21-5
2j = 16
Divide by 2
2j/2 =16/2
j =8