Answer
The materials should be heated to a temperature of $423^{\circ}C$
Work Step by Step
We can find the required change in diameter of the hole relative to the change in diameter of the bolt:
$\Delta L = 1.0000~cm-0.9980~cm = 0.002~cm$
We can find an expression for increase in diameter of the hole $\Delta L_h$ when it is heated:
$\Delta L_h = \alpha_h~\Delta T~L_h$
We can find an expression for increase in diameter of the bolt $\Delta L_b$ when it is heated:
$\Delta L_b = \alpha_b~\Delta T~L_b$
Note that when the washer fits over the bolt, $\Delta L_h-\Delta L_b = 0.002~cm$, We can find the required change in temperature:
$\Delta L_h-\Delta L_b = 0.002~cm$
$\alpha_h~\Delta T~L_h - \alpha_b~\Delta T~L_b = 0.002~cm$
$\Delta T = \frac{0.002~cm}{\alpha_h~L_h - \alpha_b~L_b}$
$\Delta T = \frac{0.002~cm}{(17\times 10^{-6}~K^{-1})(0.9980~cm) - (12\times 10^{-6}~K^{-1})~(1.0000~cm)}$
$\Delta T = 403~K$
$\Delta T = 403^{\circ}C$
The required increase in temperature is $403^{\circ}C$, so the materials should be heated to a temperature of $423^{\circ}C$
