, where is a constant and varies directly with . Given that when , and when , determine when .
Step 1: varies directly with :
where is a constant.
Substitute into :
Step 2: Use and the given conditions to create a system.
Then solve that system to find the values of and .
So, when :
and when :
Step 3: Substitute and into :
Step 4: Substitute into to find :
Therefore, when , .