5 blueberries for every 2 blackberries
black=x blue=y
140= 2x + 5y
-5y -5y
-5y + 140= 2x (divide everything by 2 to get x by itself
-2.5y +70= x (plug in to find Y)
140= -2.5 + 70 + 5y
-70 -70
70= 2.5y (divide by 2.5)
28=Y
plug in to find x......again XD
140= 2x + 28
-28 -28
112= 2x (divide by 2)
56=x
28 blueberries and 56 blackberries
i accidentally made it longer than i intended to, i am pretty sure there is a better way to do this, but i hope i helped you somehow