Solució: \begin{align} η_{total} &= \cssId{Step1}{ η_{eng} · η_{cad}} \\[3px] &\cssId{Step2}{ η_{total} = \frac {P_{roda}}{P_{motor}}} \\[3px] &\cssId{Step3}{ P_{roda} = P_{motor} · η_{eng} · η_{cad}} \\[3px] \end{align}