Answer: B, 2.4 Units
Explanation: Since the two triangles are similar, the lengths of the triangles are equal in ratio. This equates to:
AB/DE = AC/DF
since the value of AB/DE IS 5/3, the ratio between AC and DF are the same.
Substitute the ratio with the values of AC and DF, and you will get the value of DF.
If you don't understand feel free to look at my workings
