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 
D. The economy of the Soviet Union was falling behind that of other major industrialized nations.
Answer:
Number of coupons sent to Existing members = 33
Step-by-step explanation:
Number of coupons sent out = 231
Let :
6 times as many to potential members = 6 * X = 6X
while existing members = X
therefore 6X + X = 231
7X = 231
therefore X = 231 / 7 = 33
so existing members = 33
while potential members = 6 * 33 = 198
Rewriting the equation as a quadratic equation equal to zero:
x^2 - x - 30 = 0
We need two numbers whose sum is -1 and whose product is -30. In this case, it would have to be 5 and -6. Therefore we can also write our equation in the factored form
(x + 5)(x - 6) = 0
Now we have a product of two expressions that is equal to zero, which means any x value that makes either (x + 5) or (x - 6) zero will make their product zero.
x + 5 = 0 => x = -5
x - 6 = 0 => x = 6
Therefore, our solutions are x = -5 and x = 6.
Then it is likely that the amount of mice will decrease and either keep going down because the organism is eating them off too quickly or stay at a medium rate