S = n/2 (a+1)

The subject of the formula is L

Same as before, please include workings TYVM

3 answers

There is no L in your formula.
You seem to be confusing 1, l and L.

You still need to know how to use parentheses to avoid ambiguity in typed equations.
Oh sorry yes that's what i mean:

S = (n/2)*(a+L)
S = (n/2)*(a+L)
S/(n/2) = a + L
2*S / n = a + L
(2*S / n) - a = L , or
L = (2*S / n) - a