Implied volatility is changed (reduced) by 0.18 points and vega is 7.5.
So how many points will be changed (if all Greeks are not changed) in premium?
Vega is indicator of change in price of an option to 1% change in IV.
Eg. An option is priced 100 with IV 50 and Vega 10, if all things remain constant and IV drops to 49 ie. 2% option’s price will fall by 20 ie. from 100 to 80.
In your case, if your option is priced at 100, with Vega 7.5 and IV 18. If IV drops by 0.18 your Options value will reduce by 7.5 to 92.5.
You can learn in detail here.