(7a^2 + 2a - 3)(4a^2 - 1) = 28a^4 +ma^3 - 19a^2 - 2a + 3
4a^2(7a^2 + 2a - 3) - 1(7a^2 + 2a - 3) = 28a^4 +ma^3 - 19a^2 - 2a + 3
28a^4 + 8a^3 - 12a^2 - 7a^2 - 2a + 3 = 28a^4 +ma^3 - 19a^2 - 2a + 3
28a^4 + 8a^3 - 19a^2 - 2a + 3 = 28a^4 +ma^3 - 19a^2 - 2a + 3
Cancel all the same terms
8a^3 = ma^3
Therefore, m = 8