I do not understand how my answer is wrong please help will give brainly

Answer:
16
Step-by-step explanation:
angle 6 and angle 3 are supplementary angles
that means added together, they equal 180
so 8x-13 + 4x+1=180
12x-12=180 simplify by adding and subtracting
12x=192 simplify by adding 12
x=16 divide 192 by 12