Eric had 7 times as many markers as Andy. After Eric gave Andy some of his markers, each boy then had 36. How many markers had Eric given to Andy?
7/9 of 108 is 84 so 108-84 is 24 so that means 24 coins are quarters
e = 7a
e-s = 36 and a+s = 36 where 's' is 'some'
e = 36+s a = 36 -s sub these into the red equation
36+s = 7 ( 36-s)
s = 27