a bag has 57 blue and green marbles. there are 13 more blue marbles than green marbles. How many blue and green marbles are in the bag
green marbles --- x
blue marbles ---- 57-x
57-x - x = 13
-2x = -44
x = 22
so 22 green and 35 blues
check:
do they add up to 57 ? YES
are there 13 more blue than green ? YES