Diagonals bisect each other.

So, .

          (Substitute )

  (Distributive property)

                       (Simplify)

                            (Add 30 to each side) \ \

                             (Subtract x from each side)

                                     (Subtract: )

Use to determine the measure of MP.

Diagonals are congruent and bisect each other.

So, .

                                  (Definition of congruent segments)

                          (Substitute )

                    (Substitute )

                                  (Simplify)

The measure of MP is 40.