7 times the sum of "a" squared and "b"minus 4 times the sum of "a" squared and "b"

7*a^2 + b - 4*a^2 + b

7a^2 + b - 4a^2 + b

3a^2 + 2b

==> 7 cows minus 4 cows = 3 cows.

==> 7 rocks minus 4 rocks = 3 rocks

==> 7 of anything minus 4 of the same thing = 3 of them

==> 7 times (the sum of "a" squared and "b")

minus

4 times (the sum of "a" squared and "b")

leaves

3 times (the sum of "a" squared and "b")