Let's x be the Sammi's weight and y Buster's weight.
Then, as Buster and Sammi together weigh 112 pounds, then:

Also, Sammi weighs 8 pounds more than Buster, then:

Now, replace equation (2) into equation (1) and solve for y:

And replace the y-value into equation 2 to find x:

As x=64 and y=56, therefor Sammi weighs 64 pounds and Buster weighs 56 pounds.