help please show me how to slove

Question

In 1891, Almon B. Strowger patented a phone‐dialing machine that could connect up to 82 subscribers.
 
a. If he had tested his invention on 10 subscribers, how many different two‐party calls would such a machine permit?
 
The answer is
.
 
b. How many different two‐party calls would his machine permit for 82 subscribers?
 
The answer is

Answer 1

a.

₁₀C₂ = 10! / (2!(10 - 2)!)

b. 

₈₂C₂ = 82! / (2!(82 - 2)!)