Answer :
[tex]\begin{gathered} (a-b)^2=a^2-2ab+b^2 \\ In\text{ this case } \\ (6a-5b)^2 \\ a=6a \\ b=5b \\ (6a-5b)^2=(6a)^2-2\cdot(6a)\cdot(5b)+(-5b)^2 \\ (6a-5b)^2=36a^2-60ab+25b^2 \\ \text{The expanded square is }36a^2-60ab+25b^2 \end{gathered}[/tex]