x=9
DBC= 54°
The given angle is 90°, so we can add the other two given equations to equal 90.
7x-9+4x=90
1) Combine like terms
11x-9=90
2) Add 9 to both sides
11x=99
3) Divide 11 on both sides
x=9
Now to find the angle:
7x-9
1) Plug 9 in for x (which is what we just solved for)
7(9)-9
2) multiply
63-9
3) subtract
54
m= 54°
