Answer:
The longest side is 330.9 units.
Explanation:
Since the triangles are similar, the ratio of the corresponding sides of two triangles is equal.
In other words,

The lengths of the sides of triangle ABC are
AB = 140 , BC = 120 , CA = 110
The length of smallest side of triangle DEF is 260.
Thus,

thus,

So, DE = 330.9 units
similarly,

So, EF = 283.636 units
Thus the sides of triangle are 260, 283.636 and 330.9 units.
The longest side is 330.9 units.