I hope this helps you 
n=2/3-1/7
n=2.7/3.7-1.3/7.3
n=14/21-3/21
n=11/21
        
             
        
        
        
Answer:
140
Step-by-step explanation:
Suppose,
x drinks were sold for 2$
y drinks were sold for 5$
therefore, x+y = 250....( 1 )
and 2x+5y = 830......( 2 )
multiply equation ( 1 ) with 2,
2x+2y = 500......( 3 )
Subtract equation ( 3) from (2)
3y = 330 
or, y = 110
so, x = 140 
so, 140 drinks were sold for 2$
 
        
             
        
        
        
Step-by-step explanation:

<h2>explanation</h2>
 the formula in use is the square of the previous number subtract 1,
ie 
