Answer:
D. 1 and 20
Step-by-step explanation:
To solve the equation, factor the quadratic and set the factors equal to 0.
d^2 - 21d + 20 becomes (d-20)(d-1) since -1*-20 = 20 and -1+-20 = -21.
Set each equal to 0 and solve for x.
d-20 = 0 d = 20
d - 1 = 0 d = 1
