Let x represent the amount of beef and y represent the amount of pork Mike used in recipe.
He used total 8 lbs of meat, so we can write:
x + y = 8
He uses 3:1 ratio of beef to pork, so we can write:
x :y = 3 : 1
x = 3y
Using this value of x in first equation, we get:
3y + y =8
4y = 8
y = 2
x = 3y = 3(2) = 6
This means Mike used 6 lbs of beef and 2 lbs of pork for his recipe