Answer
$67.8~inches$
Work Step by Step
Without Danielle:
Let $x_i$ be the height of any student. i = 1, 2, 3, ..., 14
$Mean=\frac{Σx_i}{14}=\frac{x_1+x_2+x_3+x_4+x_5+x_6+x_7+x_8+x_9+x_{10}+x_{11}+x_{12}+x_{13}+x_{14}}{14}=68.0~inches$
$Σx_i=x_1+x_2+x_3+x_4+x_5+x_6+x_7+x_8+x_9+x_{10}+x_{11}+x_{12}+x_{13}+x_{14}=14\times68.0~inches=952.0~inches$
With Danielle:
Let $x_{Danielle}$ be the height of Danielle.
$Mean=\frac{x_1+x_2+x_3+x_4+x_5+x_6+x_7+x_8+x_9+x_{10}+x_{11}+x_{12}+x_{13}+x_{14}+x_{Danielle}}{15}=\frac{952.0+65.0}{15}=67.8~inches$
