$$ \begin{aligned} 43 &= 3+(n-1)\cdot5&& \text{simplify right side} \\[1 em]43 &= 3+5n-5&& \\[1 em]43 &= 5n-2&& \text{ swap the left and right side of the equation } \\[1 em]5n-2 &= 43&& \text{ move -2 to the right } \\[1 em]5n &= 43+2&& \\[1 em]5n &= 45&& \text{ divide both sides by $ 5 $ } \\[1 em]n &= \frac{45}{5}&& \\[1 em]n &= 9&& \\[1 em] \end{aligned} $$

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