Remember that a rhombus' sides are the same length. Thus, set the two lengths equal to each other: 3x+2 = x+12. Solve for x, then put that value back into the equation. If you did if correctly, then both 3x+2 and x+12 should be the same value. Then finally take the value given by 3x+2 or x+12 and that should be the segment length.