Mr$.$ Bing owned a flat in Mong Kok, and he let it

to Mr$.$ Quit for a two$-$year lease from $1$ April $2016$

to $31$ March $2018$ at a monthly rent of $$30,000.$

Mr$.$ Quit occupied the flat up to $30$ April $2017$ and

disappeared. He did not pay rent for six months

from November $2016$ to April $2017.$ Mr$.$ Bing took

back the flat on $1$ May $2017$ and let it to Mr$.$ Lo on

$1$ September $2017$ at a monthly rent of $$15,000.$

$Mr.$ Bing was responsible for and paid rates of

$$2,500$ each quarter all the time.

What is the property tax of $\frac{2017}{18}?$

a$.$ Irrecoverable rent $-$ carried backward to

set off in $2016/17($$$55,000)$

b$.$ Irrecoverable rent $-$ carried backward

to set off in $\frac{2016}{17}($$$45,000)$

c$.$ Irrecoverable rent $-$ carried backward to

set off in $\frac{2016}{17}($$$35,000)$

d$.$ None of the other $3$ is correct