Since the 2 triangles share a diagonal.
In the first triangle with both values for a and b.
a²+ b² = c²
6² + 8² = c²
100 = c²
10 = c
then,
a² + b² = c²( for 2nd triangle)
10² + x² = 12²
12² - 10² = x²
44 = x²
6.6 = x
