Answer
a. $20^{\circ} C$.
b. $3500^{\circ} F$.
Work Step by Step
a. Use the formula on page 362.
$$\frac{5}{9}(68^{\circ} F – 32) = 20^{\circ} C $$
b. Use the formula on page 362.
$$\frac{9}{5}(1900^{\circ} C) + 32 = 3452 \approx 3500^{\circ} F $$