We introduce the notation and draw the height BE perpendicular to the CD as shown in the figure.
By condition AB = BE = 40
Then ABED is a square (all angles are straight and all sides are equal).
The triangle BCE is rectangular, therefore
by definition, tgC = BE / EC = 5/3.
40 / EC = 5/3 => EC = 40 * 3/5 = 24
DC = DE + EC
DE = AB (by definition of a square)
DC = 40 + 24 = 64
Answer: DC = 64
Remember: The process of learning a person lasts a lifetime. The value of the same knowledge for different people may be different, it is determined by their individual characteristics and needs. Therefore, knowledge is always needed at any age and position.