In a parallelogram, the diagonals bisect each other. Therefore, the lengths of segments from the vertices to the intersection point are half of the lengths of the diagonals.
Given:
- \( RV = y + 18 \)
- \( TV = 3y - 10 \)
Since \( RV = TV \), we can set up the equation:
\[ y + 18 = 3y - 10 \]
Now, solve for \( y \):
-
Rearranging the equation gives: \[ 18 + 10 = 3y - y \] \[ 28 = 2y \]
-
Divide both sides by 2: \[ y = 14 \]
Now substitute \( y \) back into the expressions for \( RV \) and \( TV \):
\[ RV = 14 + 18 = 32 \] \[ TV = 3(14) - 10 = 42 - 10 = 32 \]
Since both segment lengths equal 32, we find \( RT \) (the whole diagonal) by doubling the length of either segment:
\[ RT = RV + TV = RV + RV = 32 + 32 = 64 \]
Thus, the length of diagonal \( RT \) is:
\[ \boxed{64} \]