Answer: D, 6km/hr.
Step-by-step explanation:
Heather can finish a 12-kilometer race in 2 hours, and now we have to find how many kilometers she can ride/run at in 1 hour.
How many hours can Heather run in 1 hour? To solve that, we can use the equation 12 ÷ 2.
12 ÷ 2 = 6.
Therefore, if Heather keeps her pace constant, then her rate will be 6km/hr, or D.