Start with

Add 2x to both sides:

Subtract 21 from both sides:

Divide both sides by 5. Since it is positive, we don't have to change the inequality sign:

So, the answer is 
If n = the term number, then:
A(4) = 6-4(4-1)
A(4) = 6-4(3)
A(4) = 6-12
A(4) = -6
A = -1.5
The equation in slope intercept form is y=-x-5
Answer: 30^2 * pi = 2827.43.