Remark
A kite has the very odd property that when the diagonal lengths are multiplied together and divided by 2, the Result is the area. Without that property, you would not have enough information.
Formula
Area = 1/2 * d1 * d2
Givens
d1 = 5
d2 = 10
Solution
Area = 1/2 * 5 * 10
Area = 1/2 50
Area = 25 <<<<<<<< Answer