Question

Suppose you make a 4-minute local call using a calling card and are charged 7.6 cents. The cost of a local call varies directly with the length of the call. How much more will it cost to make a 30-minute local call?

-Which quantity is the dependent quantity?
-How does the word "more" affect the method needed to solve the problem?

Answer 1

C = kl
The cost of a local call is the dependent variable.

The mord more means that we are looking for the additional cost to make a 30 minutes call from a 4 minutes call, or the cost of a 26 minutes call.