Answer:
10
Explanation:
128 is a supplementary angle. Supplementary angles always equal 180°.
Subtract 128 from 180
180 - 128
= 52
You now know one angle of the triangle (52). Let's find x now.
Triangles always equal 180°.
Set 4x + 3, 9x -5, and 52 equal to 180
4x + 3 + 9x -5 + 52 = 180
Combine like terms
4x + 3 + 9x -5 + 52 = 180
13x + 3 - 5 + 52 = 180
13x + 50 = 180
Subtract 50 to both sides
13x + 50 -50 = 180 -50
13x = 130
Divide by 13 to both sides
13x ÷13 = 130 ÷13
x = 10
Hope this helps and have a good rest of your day! :)