From equation 1 to equation 3

Expand the following: \begin{align} &\cssId{Step1}{{ I_{LED,3}=?}}\\[3px] &\cssId{Step2}{t_{bat,4} = {U_{bateries} – 5 U_{LED}\over 3 R}}\\[3px] &\cssId{Step3}{t_{bat,4} = {3U_{bat} – 5 U_{LED}\over 3 R}}\\[3px] &\cssId{Step4}{t_{bat,4} = 0,01532 A = 15,32 mA}\\[3px] \end{align}

1. In the first step we make the equation of the force breaking with mass and acceleration
2. In the seconde step we make the equation of normal force and the gravity force
3. In the third step we make the equation of accelation with Force breaking and mass