Answer:
b=312
g=396
you can use substitution or elimination
Explanation:
(b+g=708)10
(15b+10g=8640)1
(10b+10g=7080)-
(15b+10g=8640)
10b-15b=-1560
-5b=-1560
divide both sides by -5
b=312
then substitute
b+g=708
312+g=708
g=708-312
g=396
so b=312
g=396