We know that all the sides of a square is Equal.
And we also know that a square has 4 sides.
So we take the measurement of the perimeter, which is 78.4 and divide it by 4, which is the number of sides.
to find the length of each side=
= 19.6
In conclusion 19.6 units is the length of each side.
Note: if the unit of measurement is given(for e.g: in,m,cm...), we have to include it.
Quick Check: 19.6+19.6+19.6+19.6=78.4