25^2.7 × 5^4.2 ÷ 5^5.4 = 25^?

Answer: Option E

$$\begin{array}{rl}& \text{Let }25^{2.7}\times 5^{4.2}÷5^{5.4}=25^x\\ & \text{Then, }25^{2.7}\times 5^{(4.2-5.4)}=25^x\\ & \iff 25^{2.7}\times 5^{(-1.2)}=25^x\\ & \iff 25^{2.7}\times \frac{1}{5^{1.2}}=25^x\\ & \iff \frac{{25}^{2.7}}{{\left(5^2\right)}^{0.6}}=25^x\\ & \iff \frac{{\left(25\right)}^{2.7}}{{\left(25\right)}^{0.6}}=25^x\\ & \iff 25^x=25^{\left(2.7-0.6\right)}=25^{2.1}\\ & \iff x=2.1\end{array}$$