They are all junior high school questions, of which the 67th question is a binary quadratic equation group and the 69th question is a univariate linear equation group.

67: Suppose two balls have X boxes, three balls have Y boxes, and one ball has16-X-Y.

From the meaning of the title: x+y = 16-x-y and1x (16-x-y)+2x+3y = 27.

To solve this system of equations, x=5 and y=3, so the answer is C.

69: There are (84-x) girls for every x boys, because now the sum of boys' ages is three times that of girls, and after three years, boys are 36 years younger than girls. That is to say, in these three years, the sum of the annual aging of boys is three times less than that of girls, 12, so we can list the equation: x = 3 (84-x)- 12, and get x=60, so we choose C.