[tex] \frac{oc}{oa} = \frac{od}{ob} = \frac{cd}{ab} [/tex]
OA + AC = OC
40 + 1960 = 2000 cm
OC/OA = DC/BA
DC = BA × OC ÷ OA
DC = 30 × 2000 ÷ 40
DC = 1500 cm = 15m
