Ineed again this is really hard and i don't understand how to do it

C=10 & P=5
3C+4P=50
C+P=15
Solve
3C+4P=50
3C+3P=45
Subtract
P=5
Substitute in equation 2
C+P=15
C+5=15
C=10

Use algebra Set up a system of equations.
Let x = number of pounds of chicken he sold 
and y = number of pounds of pork 
So one equation is 
x + y = 15 (1)
And the other equation is the amount of money he made :-
3x + 4y = 50(2)

Now solve this sytem of 2 equations:-

multiply the eqaution (1) by -3:-

-3x - 3y = -45 (3)
3x  + 4y = 50 (2)   Now add (3) and (2);-

y = 5      so he sold 5 pounds of pork 

and substituting in equation (1)

x + 5 = 15 
x = 10 

So he sold 5 pounds of pork and 10 pounsd of chicken.

The answer is all about the number 4