First draw a straight line and plot the four points A,B,C,D on that line. It doesn't matter where you plot the points as long as they are in order and none overlap.
We're given AD = x+203. We also know that BD = x+127. Since AB + BD = AD (segment addition postulate) we can determine the length of AB
AB + BD = AD
AB + BD-BD = AD-BD Subtract BD from both sides.
AB = AD-BD
AB = (x+203)-(x+127)
AB = x+203-x-127
AB = 76
The length of BC is also 76 (given). So,
AB+BC = 76+76 = 152
this is equal to the length of AC because AB+BC = AC
So, AC = 152 units
Final Answer: 152 units
