Lets call the number 'n'
plus means addition
is means the equal sign
so that as an expression would be

n+4=7
Fill in the spaces in this order and it should be right
1. 15
2. 9
3. 3
4. -3
Answer:
the expression is: 
and 2730 different ways are possible.
Step-by-step explanation:
In the given question we have to choose a president, vice
president, and secretary.
Permutations are used when order is important so, as in the given question order is required. We would use permutations
The formula used is:
where:
n=total number of objects
r=number of objects selected
In our case: n=15, r=3
Putting values and finding the answer:

So, the expression is: 
and 2730 different ways are possible.