We are given: \(\displaystyle{\left({3}{t}^{{2}}−{4}{s}\right)}^{{2}}\)

Use the rule: \(\displaystyle{\left({a}-{b}\right)}^{{2}}={a}^{{2}}-{2}{a}{b}+{b}^{{2}}\) where \(\displaystyle{a}={3}{t}^{{2}}\) and \(b=4s\)

\(=((3t^2)^2)-2(3t^2)(4s)+(4s)^2 =9t^4-24t^2\times s+16s^2\)