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