Explanation:
the diagonals of a parallelogram are crossing each other exactly at their midpoints. that means the lengths of both sides of a diagonal are equal.
so, we get
x = 7y - 16
and
2x + 5 = 5y
we can use the first equation as an identity directly in the second equation and get
2(7y - 16) + 5 = 5y
14y - 32 + 5 = 5y
14y - 27 = 5y
9y - 27 = 0
9y = 27
y = 3
x = 7y - 16 = 7×3 - 16 = 21 - 16 = 5