Can someone please help me with this problem? This is what I have but I am not sure that it is proof.

RT=12 and TD = 4 which makes RD=16

The ratio of RT to RD is12

16

This is reduced to3

4

RS= 9 and SC=3 which makes RC=12

The ratio of RS to RC is9

12

This is reduced to3

4

The ratio of RT to RD equals the ratio of RS to RC which makes the lines TS and DC parallel.