Answer:
If I read this diagram correctly then
DE 9x - 31 y implies that the slope y / x = 9/31 = .29
and arctan .29 = 16 deg
and line CD 7x - 2y implies that slope y / x = 7/2 = 3.5
and arctan 3.5 = 74 deg
So in that interpretation the difference is 58 deg
But, I'm not certain of the terminology being used.
