Answer:
x = 34
Step-by-step explanation:
From the picture we have
AD = CD = BC = AB
it's enough to say that this quadrangle is a rhombus.
The diagonals in each rhombus are perpendicular and divide to half.
Therefore we have the equation:
3x - 12 = 90 add 12 to both sides
3x - 12 + 12 = 90 + 12
3x = 102 divide both sides by 3
3x : 3 = 102 : 3
x = 34
