Just divide the percentage by the amount they are asking
So basically you want to isolate only one of the variable on one side so
y=-9+x^2
add 9 to both sides
y+9=x^2
square root both sides

x=
Answer:
13.8
Step-by-step explanation:
Recall the trigonometric ratios
Sine = Opposite over Hypotenuse (SOH)
Cosine = Adjacent over Hypotenuse (CAH)
Tangent = Opposite over Adjacent (TOA)
Now lets look back at the question
We are given an angle and its adjacent side length (11) and we need to find the hypotenuse
The hypotenuse and adjacent sides corresponds with the trig function cosine so we will use cosine to solve for x
( remember that cosine = adjacent over hypotenuse )

step 1 multiply each side by x

now we have 
step 2 divide each side by cos(37)

we're left with x = 13.77439
Our last step would be to round to the nearest tenth
We would get that the answer is 13.8
Suppose x grams of 8% solution should be mixed to make 100 g of 3% solution.
here we shall have:
the amount of 3% solution in the 100 g will be:
3/100*100=3 grams
the the equation will be, 8% of what quantity becomes 3g?
(8/100)*x=3
hence solving for x we shall have:
0.08x=3
x=3/0.08
x= 37.8 grams
The implication of this is that, when you have 37.5 grams of 8% solution, that will contain 3 of pure chemical and hence when you add more solvent on top of 37.5 g until you reach 100g, that will be 3% solution.