What is the fourth number of 12 48 50 if the mean is 30

Alice is paying her bill at a restaurant. but tax on the cost of a male is 5%. she decides to leave a tip 20% of the cost of the meal plus the tax

Factor 15x^3 - 5x^2 +6x-2 by grouping. what is the resulting expression

Answer this all of it i don’t know how to do it i wasn’t there because i was sick and it’s a nti today so i home not knowing what to do