Answer:
The length of the longest side is 13mm
Explanation:
Represent the two sides with a and b, where a is the longest


Required
Determine the length of the longest side
Perimeter of a kite is calculated as thus:

Make b the subject in


Substitute a - 1 for b and 50 for Perimeter in


Divide through by 2


Add 1 to both sides



Solve for a


Hence, the length of the longest side is 13mm