Question

How do I solve for c and d

Answer 1

For c using proportionality of corresponding sides you can writing 

(3c+4)       9
--------- = -------
    20         15

(3c+4)       3
---------- = ------    cross multiple 
    20          5

5(3c+4) = 20*3   divide both sides by 5

3c+4=4*3

3c+4=12

3c = 8

c = 8/3

for d you can writing 

(2d-3)       9
--------- = ------
   12          15

(2d-3)       3
--------- = -------   cross multiple 
   12          5

5(2d-3) = 12*3

10d -15 = 36

10d = 51

d = 51/10

d = 5,1

hope helped