Point c(3.6, -0.4) divides ab in the ratio 3: 2. if the coordinates of a are (-6, 5), the coordinates of point b are if point d divides cb in the ratio 4 : 5, the coordinates of point d are

When a point divides a line segment into ratios of k1:k2, the formula to find the coordiates of the point is:
x=(k2*x1+k1*x2)/(k1+k2), y=(k2*y1+k1*y2)/(k1+k2), 
(x1,y1) being the coordinates of the starting point, and (x2,y2) coordinates of the end point. 
in this case, 3.6=[2*(-6)+3x2]/5
-12+3x2=18
3x2=30
x2=10

use the same method to find y2: -0.4=(2*5+3y2)/5
3y2=-12
y2=-4
so the the coordinates of B is (10,-4)

use the same method to find the coordinates of D.

the answer I've got for D is (58/9, -2) please double check my calculation.

That little box would be 90 degrees. a triangle should be 180 degrees. 90 + 15= 105. 180-105=75. your answer would be 75 degrees but since you asked for the nearest tenth, it would be 80 degrees.