DC=6x and DA=4x+18, and DC=DA, so 6x=4x+18. then you need all the x's on one side so subtract 4x and you get: 2x=18 then divide by 2: x=9 now that you now what x is you can plug it in for DC and DA: DC=6(9) DC= 54 *since DC=DA you should also get 54 for DA but do the math to make sure ;) DA=4(9)+18 DA=36+18 DA=54 *AC=DC+DA, you know this because D is the midpoint between A and C, on a line they would show up in the order ADC. AC=54+54 AC=108 so... x=9, DC=54, DA=54, and AC=108