Answer: x = 3π/2
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We are given:

Our goal in solving for any variable, in this case is x, we need to isolate x on one side of the variable. Let's start by subtracting 7x from both sides, which will cancel the +7x on the right side. We are then left with:

Now, we want to move that +10 to the other side so our x is all by itself. Let's subtract 10 from both sides, which will cancel the +10 on the right leaving us with:

Since we cannot have a coefficient when solving for x, we need to divide both sides by -3.

When we divide, our answer is:

y = x^2 + 2x...eqn 1
y = 3x + 20...eqn 2
subst for y in eqn 1...
=> x^2 +2x = 3x +20
=> x^2 - x - 20 =0
=> (x-5) (x+4) =0
=> x = 5 or -4
for x =5, y = 35 (sub for x in eqn 1 or 2)
for x = -4, y = 8 (sub for x in eqn 1 or 2)
Solve for m:C = 1/3 π d^2 m
C = 1/3 d^2 m π is equivalent to 1/3 d^2 m π = C:1/3 π d^2 m = C
Divide both sides by (π d^2)/3:Answer: m = (3 C)/(π d^2)