Which equations are correct? Select each correct answer.

−4b3(5b2+3)=−20b6−12b3

−6y4(4y2+2)=−24y8−12y4

−5a4(2a2+4)=−10a6−20a4

−4x2(2x2+5)=−8x4−20x2

Weekly wages at a certain factory are normally distributed with a mean of $400 and a standard deviation of $50. find the probability that a worker selected at random makes between $450 and $500