solve 0= p^5 (1300/5 - 280) + 4 p^4(1-p) (1300/4 - 280) + 6 p^3(1-p)^2 (1300/3 - 280) + 4 p^2(1-p)^3 (1300/2 - 280) + p (1-p)^4 (1300 - 280) for p