Question 284673
There are infinite number of triangles that could have a perimeter of 78 cm.
another poorly worded problem or poorly copied problem.

if 28 is the base then the equal sides are 25 each 
if the base is not 28 then the other equal side is also 28 78-56=22
So one triangle would be 25, 25  and 28
the other would be 28, 28 and 22