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