So it's length would be half of the length of the base [tex] \frac{14}{2} [/tex] = 7 => [tex] 7^{2} [/tex] + [tex] x^{2} [/tex] = [tex] 14^{2} [/tex] => 49 + = 196 => x^2 = 147 => x = sqrt 147 = 7 * sqrt 3 . So the altitude is equal to 7 * sqrt 3. An approximate value to that would be 12.12
Hope this helps