Answer:
6 days. I think it's probably reasonable if his objective is to break even. See discussion below.
Explanation:
Costs
Rent          2000
raw materials           75
Advertising            25
Total Costs = 2000 + (75 + 25)x
Total Costs = 2000 + 100x
Revenue
           500* x
So you want to know what value of x will cause a break even point.
2000  +  100x =  500x         Subtract 100x from both sides
2000 = 500x - 100x
2000 = 400x                 Divide by 400
x = 5
I don't know really if it is reasonable or not. But think of it this way: if he has to make 5 suits just to break even that means that he has on average about 6 days for one suit.
Anymore suits needed (like to live on) would mean that he'd have to be awfully quick with a needle and thread.