If Sierra is currently 30 years old, 10 times her age is 30*10 = <<30*10=300>>300.
Twenty more than 10 times Sierra's age is 300+20 = 320
320 is 40 less than ten times Diaz's age so 10 times Diaz's age is 320+40 = 360
If ten times Diaz's age is 360, Diaz is 360/10 = <<360/10=36>>36 years old.
Twenty years from now, Diaz will be 20+36 = <<20+36=56>>56 years old.
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