$$ \begin{aligned} 50 &= 6a+28&& \text{ swap the left and right side of the equation } \\[1 em]6a+28 &= 50&& \text{ move 28 to the right } \\[1 em]6a &= 50-28&& \\[1 em]6a &= 22&& \text{ divide both sides by $ 6 $ } \\[1 em]a &= \frac{22}{6}&& \\[1 em]a &= \frac{11}{3}&& \\[1 em] \end{aligned} $$