AHSME 1980 Problem 24

For some real number $r$, the polynomial $8x^3-4x^2-42x+45$ is divisible by $(x-r)^2$. Which of the following numbers is closest to $r$? $\text{(A)} \ 1.22 \text{(B)} \ 1.32 \text{(C)} \ 1.42 \text{(D)} \ 1.52 \text{(E)} \ 1.62$