How do you work out star magnitude?

If a star increases in brightness by a factor of 4 what is the increase in apparent magnitude? The only equation I was given is m1-m2 = 2.5log(f2/f1) but since the flux is not given I am confused. Any help would be great.

What is a VPN?

VPN is (Virtual Private Network) were first used by companies to enable their employees to securely access internal systems such as email remotely (e.g. from home or while on business trips). Today they are increasingly being used for personal use by individuals to protect their privacy while online in public places (e.g. when using the wi-fi connection in a cafe) or in a country where the internet is censored / blocked (e.g. China, Saudi Arabia…).