Question

Two numbers have a sum of 45. If one number is p, express the other number in terms if p.

Answer 1

 p + n = 45
 

subtract p from both sides

n = 45 - p 

Answer 2

Heyo Kiddo. How are you doing today? 
Let's figure this out. 

So, if "one number is p," then we can say the other number can represent the variable z. 

We can conclude that: p + z = 45
 
For us to solve for z : 
 
p + z = 45
- p       -p

So then,
z = 45 - p 
You're welcome. :)