HELP I NEED HELP ASAP HELP I NEED HELP ASAP

The function p(t)=-20t^2+80t models the profit, in thousands of dollars, of a company after t years. How many years, in total, does the company earn a profit?

A. 40
B. 2
C. 4
D. 80

The first one, i believe, would be correct. all the others have one thing in common, and that's that they have repeating numbers. in the second one, x and y have repeating 6's and 3's, and in the third, x and y have repeating 6's as well. in the last one, there are repeating 3's. the first one has no repeating numbers.