Answer:
I believe the answer is 2
Step-by-step explanation:
 
        
             
        
        
        
Let x be for unknown number. Let x be first number .
X+1 To be second number .x+2be third number.  X+(x+1)+(x+2)=312.
Simplify to get 3x+3=312 . Subtract 3 from both sides 3x-3=312-3. Once you subtract get 3x=109.then divide 3 both sides . 3x/3=309/3. To get x= 103.  
Now once you have that  First number 103. Second number 103+1=104 . And third number 103+2=105.    To check add them 103+104+105=312
 
        
             
        
        
        
I believe four is the right answer to the problem
        
             
        
        
        
Answer:
12
Step-by-step explanation:
This can be solved by working backwards.
7 is one more than half the number of invitations.
Subtract 1.  6 is half the number of invitations.
Double.
12 is the full number of invitations.
Algebra (if you must!):
x = number of invitations
x/2 + 1 = 7
Subtract 1.
x/2 = 6
Multiply by 2.
x = 12
 
        
                    
             
        
        
        
let h = horse, let c = cow, let p = pig
so, 
hcp
hpc
cph
chp
phc
pch
so, that is 6 different ways she can arrange it.