Coefficient of variation CV =std/mean *100%
CV = 3/25 *100%
Cv = 12%
There are 3 ways of solving a simultaneous problem, substitution method, elimination method and Gauss-Jordan method. I'm gonna use the substitution method since it's easier and i think it would suit your level more.
First let's try solving for y since it's easier to start with.
Firstly we have to find an equation for x:

Great, now we can use the substitution method to find the value of y using the first equation:

Now we know that y=1 we can solve the first equation we made:

And the answer is 
Double check:

And that's our final answer! (4,1)
6 / (2/3)
= 6 * 3/2
= 18/2
= 9
answer
there are 9 (2/3 cup) servings in 6 cups of yogurt
Answer:
$148.75
Step-by-step explanation:
$175 · 15% = $26.25
$175 - $26.25 = $148.75