What is VXU?
First find the value of 'x' not 'X'
9x+18 + 5x+15 + X = 15x + 3x+21 + X
4x -12 = 0
x = 3
then for triangle vxu 3(3) +21 + X + 15(3) = 180 show X = 105 degrees (this is VXU)