Answer
$MR = 125$
$RP = 125$
$MP = 250$
Work Step by Step
The diagonals of a parallelogram bisect each other. Therefore the point R is the midpoint of $\overline{MP}$
We can find the value of $a$:
$MP = 2\times MR$
$12a+34 = 2\times 5(a+7)$
$12a+34 = 10a+70$
$2a = 36$
$a = 18$
We can find $MR$:
$MR = 5(a+7) = 5(18+7) = 125$
We can find $RP$:
$RP = MR = 125$
We can find $MP$:
$MP = MR + RP = 125 + 125 = 250$
