[tex]\text{Given that,}\\\\\text{Area} = 12 b^7 b b^4 =12 b^{12}\\\\\text{Width} = 4a^2 b^2\\\\\text{Now,}\\\\\text{Length} \times \text{Width} =\text{Area} \\\\\implies \text{Length} = \dfrac{\text{Area}}{\text{Width}}=\dfrac{12b^{12}}{4a^2 b^2} = \dfrac{3b^{10}}{a^2}[/tex]
