The only way to think about this is that the $158 Alberto paid is 70% of the original price. If you save 30% you pay 70% (30% + 70% = 100%)
I will put that into math language
$158 = 70% of n or $158 = .7n Solve by dividing both sides of the equation by .7
(note that when you divide by a decimal less than 1, the answer will be larger than the starting number - $158 - which is exactly what we want.
To the nearest penny the cost of the phone is $225.71
Many people will try to find 30% of $158 and add it onto $158 but that will not work because the 30% came off the unknown price you are looking for and not the $158. You can't find 30% of a price you don't know. You must talk about it in terms of what you a paying - reread the first thing I wrote at the top of this page. You can try the wrong way yourself (finding 30% and adding it on) and when you check it, it won't work.