7times 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")