Question 1196431
<font color=black size=3>
M is the midpoint of AB, so AM = MB
and
AM+MB = AB
AM+AM = AB
2*AM = AB
AM = AB/2
AM = 20/2
AM = 10


Then,
AM = 3x+1
3x+1 = 10
3x = 10-1
3x = 9
x = 9/3
x = 3
</font>