From the question, we have:
• The function, d(t), represents the total number of miles Joanna has cycled.
,
• The variable, t, represents the number of hours after stopping for a break during her ride.
If t = 4, then Joanna stopped for 4 hours for a break during her ride.
If we substituted the value of t = 4 into the function, d(t), we have:

Then, we have that Joanna has cycled 68 miles.
Therefore, we have that (according to the directions in the question):
So, d(4) = 68. This means that after a four-hour break, Joanna cycled 68 miles in total.