Polynomials and fractions

From the given expressions choose the one, that by substituting for \( \mbox{*} \) into a trinomial \[ 9- \mbox{*} +16a^2b^4\] makes possible to express the trinomial as a square of a difference, i.e. \( (A-B)^2\).

Factor the expression: \(5ab-ac+15bd-3cd\).

Simplify the expression: \[ \frac{a-1}{2}+\frac{b+1}{3}-\frac{a+b-1}6 - \frac{b-a+1}9-\frac{b-4a}{18}\]

Simplify: \[2(3r^4 - 8r^3s - 5r^2s^2 + rs^3) - 4(2r^4 - 5r^3s + 2r^2s^2 - 6rs^3)\]