What should come in place of in the given expression?$\frac{36^{1.5}\cdot\left(216^{-\frac23}\right)}{1296^{-0.75}}$=$6^{?}$

Express everything as powers of 6: $(36)^{1.5} = (6^2)^{1.5} = 6^3$. $(216)^{-\frac{2}{3}} = (6^3)^{-\frac{2}{3}} = 6^{-2}$. $(1296)^{-0.75} = (6^4)^{-\frac{3}{4}} = 6^{-3}$. Now compute: $6^3 \times 6^{-2} \div 6^{-3} = 6^{3 + (-2) - (-3)} = 6^{1 + 3} = 6^4$. Hence, $? = 4$.