Find the mistake in one-step equations

Carly tried to solve an equation step by step. $\qquad\begin{align} 7a&=28\\\\ \\ \dfrac{7a}a&=\dfrac{28}7&\green{\text{Step } 1}\\\\ \\ 7&=4&\blue{\text{Step } 2}\\\\ \end{align}$ **Find Carly's mistake.** [[☃ radio 1]]