.
As I look at this problem, the condition seems strange to me.
This restriction "at most 100 gadgets per day", actually, does not work,
since it is overlayed by other restrictions on available time.
Even if suppose, that this restriction is a fictive essence, then the solution
for the problem can be easily get MENTALLY.
Indeed, there is only three competitive cases:
(1) 4 regular, 0 premium gadget, giving 4*20 = 80 dollars profit;
(2) 0 regular, 2 premium gadgets, giving 2*30 = 60 dollars profit;
(3) 2 regular, 1 premium gadgets, giving 2*20 + 30 = 70 dollars profit.
My interior feeling is that the numbers in the problem are INCORRECT.
Last several days, I see several posts at the forum with incorrect input data.
My impression is that in the opposite end of the internet there is a person,
which specially/intently corrupts data in incoming posts.
This my message is to the MANAGERS of this project.