Question

5asquare +2asquare-asquare+7asquare

Answer 1

$5a {}^{2} + 2a {}^{2} - a {}^{2} + 7a {}^{2}$
$= \: 5a {}^{2} + a {}^{2} + 7a {}^{2}$
$= \: 13a {}^{2}$