Which equation can be solved by using this system of equations?

\[ y = 3x^3 - 7x^2 + 5 \]
\[ y = 7x^4 + 2x \]

A. \[ 3x^3 - 7x^2 + 5 = 0 \]
B. \[ 3x^3 - 7x^2 + 5 = 7x^4 + 2x \]
C. \[ 7x^4 + 2x = 0 \]
D. \[ 7x^4 + 3x^3 - 7x^2 + 2x + 5 = 0 \]