it is a geometric situation and the formula is the following 

so after 6 hours we get 
 
 
        
             
        
        
        
Answer:
y = 28
Step-by-step explanation:
Given that y varies directly as x and inversely as z then the equation relating them is
y =  ← k is the constant of variation
 ← k is the constant of variation
To find k use the condition y = 4 when x = 2 and z = 7, then
4 =  ( multiply both sides by 7 )
 ( multiply both sides by 7 )
28 = 2k ( divide both sides by 2 )
14 = k
y =  ← equation of variation
 ← equation of variation
When x = 6 and z = 3 , then
y =  = 14 × 2 = 28
 = 14 × 2 = 28
 
        
             
        
        
        
D................................l
        
             
        
        
        
Answer:
£80
Step-by-step explanation:
larger ratio is 15 and smaller ratio is 1
15 + 1 = 16
£5×16=£80
 
        
             
        
        
        
I don't know how you expand it but the answer is 3x + 25 unless that's expanding.