Problem

Cyrus solved a quadratic equation. His work is shown below.
In which step did Cyrus make an error?
13(x1)2=12(x1)2=36Step 1x1=6Step 2x=7Step 3\begin{aligned} \dfrac{1}{3}(x-1)^2&=12 \\\\ (x-1)^2&=36&\text{Step }1 \\\\ x-1&=6&\text{Step }2 \\\\ x&=7&\text{Step }3 \end{aligned}
Please choose from one of the following options.