Answer:
A
Step-by-step explanation:
6x + 12x + 90 = 180
Well 6x plus 12x must equal 90 degrees. 6x plus 12x plus 90 has to equal 180.
Therefore, 6x + 12x + 90 = 180
Because then, if you subtract 90 from both sides, you have that 6x + 12x = 90.
