It all depends on the importance of the variable its self. Its important to solve it so you know what the variable is and its important to solve one at a time because its impossible to solve a variable completely if you have two of them
Answer:

Step-by-step explanation:
Pythagorean Theorem: 
In this case, a = 9, b = a, and c = 15.


The, we subtract 81 from both sides getting:
,
Then, 
Answer:
28
Step-by-step explanation:
First, find the ratio between the triangles. To do this, divide any side of the big triangle by corresponding side in the small triangle. I chose 35. So, 35/10 = 3.5. 3.5 is the ratio between the triangles. Multiply 3.5 by 8 to get 28, the length of the missing side. :)
<h3>
Answer: 1</h3>
Explanation:
The jump from 2 to 2&1/2 is an increase of 1/2
2 + 1/2 = 2 & 1/2
The jump from 2 & 1/2 to 1 & 1/2 is a decrease of 1
(2 & 1/2) - 1 = (2 - 1) & 1/2 = 1 & 1/2
The jump from 1 & 1/2 to 2 is an increase of 1/2
(1 & 1/2) + 1/2 = 1 + (1/2 + 1/2) = 1 + 1 = 2
The pattern seems to be "add 1/2, subtract 1". Assuming this is the case, we would then subtract 1 from the last term we got (2) to get 2-1 = 1
Could you provide more details about mixtures B and C :)?