Ravi's neighbor remember to water the plant = $\frac{9}{10}$
Ravi's neighbor forgot to water the plant = $\frac{1}{10}$
With water,
Probability that plant dies = $\frac{3}{20}$
Without water,
Probability that plant dies = $\frac{4}{5}$
the probability that Ravi's neighbor forgot to water the plant if given that plant is actually died is
by bayes' theroem,
= $\frac{\frac{1}{10}*\frac{4}{5}}{(\frac{1}{10}*\frac{4}{5}) + (\frac{9}{10}*\frac{3}{20})} = \frac{\frac{4}{50}}{\frac{4}{50}+\frac{27}{200}} = \frac{\frac{4}{50}}{\frac{43}{200}} = \frac{16}{43}$
Option C.