Answer
$11x^4 -18x^2+5$
Work Step by Step
We simplify by removing the parentheses and then add the like terms as follows:
$$
(3x^4 - 5x^2 + 4) + (6x^4 - 6x^2 + 1) + (2x^4 - 7x^2)\\
=3x^4 - 5x^2 + 4 + 6x^4 - 6x^2 + 1 + 2x^4 - 7x^2\\
=11x^4 -18x^2+5
.$$
