Answer:
C
Step-by-step explanation:
This is a linear equation in one variable and has 1 solution
12x + 6 = 5x ( subtract 5x from both sides )
7x + 6 = 0 ( subtract 6 from both sides )
7x = - 6 ( divide both sides by 7 )
x = - [tex]\frac{6}{7}[/tex] ← 1 solution
