$6.$ If the catalytic reforming process increases the octane number of naphtha from $60$ to $95,$ and the refinery processes $20,000$ barrels per day of naphtha, calculate the increase in the octane number per barrel.

a$)1\mathrm{.}75$

b$)1\mathrm{.}65$

c$)1\mathrm{.}55$

d$)1\mathrm{.}45$