So represent missing number with x
x means unknown so 
x+-1=+1
adding a negative means subtraction
x-1=1
you can do anything to an equation as long as you do it to both sides
add 1 to both sides
x+1-1=1+1
x+0=2
x=2
the number is 2
        
             
        
        
        
<span>The slope of the line is equal to (y - 7) / (x - 4)
Then we can set up this equation:
(y - 7) / (x - 4) = 3
y - 7 = 3 * (x - 4)
y - 7 = 3x - 12
y = 3x - 5
This is the equation of the line.</span>
        
             
        
        
        
 A snowflake falls 90 feet in 1 minute.
60 ÷ 4 = 15
6 x 15 = 90
 
        
             
        
        
        
Hello there! 
You can use the equation:
504 ÷ 6
84
The hotel can buy 84 pillows.
Hope this helped! :D