For this case we have the following polynomials:
 [tex]3x ^ 2 + 4
x ^ 2 + 2x + 5[/tex]
 Subtracting both polynomials we have:
 [tex](3x ^ 2 + 4) - (x ^ 2 + 2x + 5)
[/tex]
 Subtracting terms from the same exponent we have:
 [tex]x ^ 2 (3-1) - 2x + (4-5)
[/tex]
 Rewriting we have:
 [tex]2x ^ 2 - 2x - 1
[/tex]
 Answer:
 [tex]2x ^ 2 - 2x - 1[/tex] will be a polynomial