There were baseballs, tennis balls and softballs in a basket. 2/7 of the balls were baseballs. There were 21 fewer tennis balls than baseballs. The rest wer 54 softballs. How many balls were there in the basket altogether?
b = 2/7 * (b + t + s)
t = b - 21, s = 54
=> b = 2/7 * (b + b - 21 + 54) = 2/7 (2b + 33)
b = 4b/7 + 33/7
=> b - 4b/7 = 33/7
=> (7b - 4b) = 33
=> 7b - 4b = 33
=> 3b = 33
=> b = 11
