Let's solve this problem step by step.
First. The sum of a squared and b
\(a^2+b\)
Second. 7 times the sum of a squared and b
\(7(a^2+b)\)
Third. 4 times the sum of a squared and b
\(4(a^2+b)\)
Finally. 7 times the sum of a squared and b minus 4 times the sum of a squared and b
\(7(a^2+b)-4(a^2+b)\)
And this is:
\(\boxed{7(a^2+b)-4(a^2+b)=3(a^2+b)}\)
