Using addition or subtraction math problem

How do u solve this using addition or subtraction??

Daniele has 18 marbles. All the marbles are either black or gold. There are 4 more gold marbles than black . How many black marbles are there?

Actually you have to set up some equations,
lets have B= # of Black marbles and G= # of Gold marbles
B+4=G
G+B=18----->this can be rewritten as: B-18=-G
Next, get rid of the G (or the B, either one is fine) by combining two equations like this:
B-18=-G
+ B+4=G
---------------------
2B-14=0
next figure out B:
2B=14
B=7 Marbles
then plug B into B+4=G for G:
G=11 Marbles
Hope this helps