Answer:
Other diagonal is 98.5 inches long.
Step-by-step explanation:
Formula to get the measure of diagonals of a parallelogram is,

where x and y are the lengths of the diagonals and a and b is the measure of two non parallel sides.
If a = 50 inches, b = 80 inches and x = 90 inches,
then from the given formula,
90² + y² = 2(50² + 80²)
y² = 2(2500 + 6400) - 8100
y² = 17800 - 8100
y = 
y = 98.49
≈ 98.5 inches
Therefore, other diagonal of the parallelogram is 98.5 inches long.