A=48
Explanation
Two Angles are Supplementary when they add up to 180 degrees
Step 1
if A and B are supplementary angles, then
[tex]A+B=180[/tex]Let
A=4x-16
B=8x+4
Step 2
replace,
[tex]\begin{gathered} A+B=180 \\ 4x-16+8x+4=180 \\ 12x-12=180 \end{gathered}[/tex]Step 3
solve for x
[tex]\begin{gathered} 12x-12=180 \\ 12x=180+12 \\ 12x=192 \\ x=\frac{192}{12} \\ x=16 \\ \end{gathered}[/tex]Step 4
finally, replace the value of x= 16 to find A
[tex]\begin{gathered} A=4x-16 \\ A=4(16)-16 \\ A=64-16 \\ A=48 \end{gathered}[/tex]