In a normally distributed data set a mean of 55 where 99.7% of the data fall between 47.5 and 62.5, what would be the standard deviation of that data set?

Answer asap! show all work! find the number of complex roots, the possible number of real roots and the possible rational roots of the polynomial function. then, solve for all roots. x^3 + 2x^2 + 3x + 6 = 0