28 should be multiplied by to get a perfect square

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!

:)