Answer:
There are plenty of numbers that can multiply with 28 to create a perfect square.
The smallest perfect square could be created as following:
We have: 28 = 4 x 7 = 2^2 x 7 (2 and 7 are prime numbers).
=> Another 7 is left to create a perfect square.
=> The smallest one among possible solutions is 7
Check:
28 x 7 = 196 = 16^2 (valid)
Hope this helps!
:)