boberon [tex]\dfrac{(7a^2)^4\cdot(7a^3)^5}{a^2(49a^8)^3}=\dfrac{7^4a^8\cdot7^5a^{15}}{a^2\cdot49^3a^{24}}=\dfrac{7^9a^{23}}{7^6a^{26}}=\dfrac{7^3}{a^3}=\left(\dfrac{7}{a}\right)^3=\left(\dfrac{7}{3.5}\right)^3=2^3=8[/tex]