Answer:
(L-a)/d + 1 = n
Step-by-step explanation:
Let's isolate (n-1), and after that isolate n:
1) subtract a from both sides: L - a = (n-1)d
2) Divide both sides by d: (L-a)/d = n-1
3) Add 1 to both sides, to isolate n: (L-a)/d + 1 = n
