Answer
7$a^{2}$ + 7ab + 3 $b^{2}$
Work Step by Step
( $a^{2}$ - ab + 4$b^{2}$ ) + (6$a^{2}$ + 8ab - $b^{2}$
$a^{2}$ - ab + 4$b^{2}$ + 6$a^{2}$ + 8ab - $b^{2}$
$a^{2}$ + 6$a^{2}$ -ab + 8ab + 4$b^{2}$- $b^{2}$
combine like terms
7$a^{2}$ + 7ab + 3 $b^{2}$ simplify