Solució: \begin{align} E = P · t & \cssId{Step1}{ -> També~sabem~que: } \\[3px] &\cssId{Step2}{E_{potencial} = m·g·Δh} \\[3px] &\cssId{Step3}{P_{mec} = \frac{E_{potenical}}{t}} \\[3px] &\cssId{Step4}{P_{mec} = \frac{m·g·Δh}{t}} \\[3px] \end{align}