5n^2 - 3n - 2 + (-7n^2 + n + 2), " Adding first two terms"
=>5n^2 - 3n - 2 - 7n^2 + n + 2, " removing bracket"
=>5n^2 - 7n^2 - 3n + n - cancel 2 + cancel 2, " rearranging like terms together"
=>-2n^2 -2n
-2n^2 - 2n - (12n^2 -n + 9, " subtracting the tnird term from the result"
=> - 2n^2 - 2n - 12n^2 + n - 9, " removing bracket"
=> -2n^2 - 12n^2 - 2n + n - 9, " rearranging terms"
color(brown)(=> -14n^2 -n - 9