Six small marbles and four large marbles have a combined weight of 30 g, whilst seven small marbles and two large marbles have a weight of 23 g. Find the weight of a large marble.

Question

Can someone help me create the equation? Thanks.

Answer 1

Just like it says:

6s +4l = 30 ---as is ---> 6s + 4l = 30
7s + 2l = 23 --times 2--> 14s + 4l = 46
subtract them:
8s = 16
s = 2

in the first ----> 12 + 4l = 30
4l = 18
l = 9/2 or 4.5

the large marble weighs 4.5 g, the smaller 2 g

Answer 2

"in the first ----> 12 + 41 = 30"

Sorry if this sounds dumb, but where does the 12 come from?