The first step for solving this problem is to multiply both sides of the bottom equation by -3.

Add the two equations together.
6x - 9y - 6x + 9y = 16 - 21
Eliminate the opposites.
-9y + 9y = 16 - 21
Remember that the sum of two opposites equals 0,, so the equation becomes the following:
0 = 16 - 21
Calculate the difference on the right side of the equation.
0 = -5
This means that the statement

is false for any value of x and y. That means that the answer to your question is (x,y) ∈ ∅,, or no solution.
Let me know if you have any further questions.
:)
Answer:
Step-by-step explanation:
1). x² - 10x + a²
By using the formula of (a - b)² = a² - 2ab + b²
x² - 2(5)x + a²
Therefore, for a perfect square of the expression a should be equal to 5.
Therefore, (x² - 10x + 25) will be the answer.
2). x² + 2ax + 36
= x² + 2(a)x + 6²
For a perfect square of the given expression value of a should be 6.
x² + 2(a)x + 6² = x² + 2(6)x + 6²
= (x + 6)²
Therefore, x² + 12x + 36 will be the answer.
3). 

To make this expression a perfect square,
a² = 
= 
Therefore, the missing number will be
.
<span>8.66666666666. I'm not sure if there are any more 6's.</span>
Given that the decay rate of the uranium is given to be 57%, this means that on the second day only 43% of the Uranium-233 will be left. The equation therefore, that will allow us to answer the question is that,
A(t) = A(0)(1 - r)^n
where A(t) is the amount after n days, A(0) is the original amount, r is the decimal equivalent of the rate and n is the number of days. Substituting the known values,
A(t) = (3,820 pounds)*(1-0.57)^15
A(t) = 0.0121 pounds
This is unfortunately not found in the choices.