We can expand our answer and compare it with the given expression.
(4a +11b) (4a - 11b)
4a (4a +11b) - 11b(4a +11b)
16 a^2 + 44ab - 11b(4a +11b)
16a^2+44ab-44ab-121b^2
16a^2-121b^2
We can see above that after expanding and simplifying, the result is the same as the given expression. Therefore, we can be sure our solution is correct!