Answer:\frac{s-a}{n-1}
Step-by-step explanation:
formula, s=a+(n-1)d
1. get rid of the a on d's side by subtracting it from both sides.
s=a+(n-1)d becomes s-a=(n-1)d
2. get rid of (n-1) by dividing it from both sides. s-a=(n-1)d becomes
\frac{s-a}{n-1} =d
