Solution: The simplest expression is 12x2−x−35.

Given: The expressionis (3x+5)(4x−7) .

Explanation: The provided expression is

(3x+5)(4x−7).

Simplify it as follows:

(3x+5)(4x−7)=3x(4x−7)+5(4x−7)=12x2−21x+20x−35=12x2−x−35

Conclusion: The simplest expression is (3x+5)(4x−7)=12x2−x−35.