SOLUTION:
Since M is the midpoint (middle) of the line AB, then AM is equal to MB.
3x + 4 = 10x - 17
Collecting like terms
4 + 17 = 10x - 3x
21 = 7x
or
7x = 21
x = 21/7
x = 3
The length AM = 3x + 4 = 3(3) + 4 = 9 + 4 = 13
The length MB = 10x - 17 = 10(3) - 17 = 30 - 17 = 13
The length AB = AM + MB = 13 + 13 = 26
M = (AM + MB) / 2
M = (13 + 13) / 2
M = 26/2
m = 13 units
