S=n/2(a+l) solve for a

1. Start with the equation: S = \frac{n}{2} (a + l)
2. Multiply both sides by 2 to get rid of the fraction: 2S = n (a + l)
3. Divide both sides by n to isolate \(a + l\): \frac{2S}{n} = a + l
4. Subtract l from both sides to solve for a: a = \frac{2S}{n} - l

So the solution is a = \frac{2S}{n} - l.