$49+0.75n$ is the correct expression.
Work Step by Step
Looking at the table, you can see that there is a single charge of \$49 no matter how many miles are driven. In addition, there is a charge of $\$0.75$ if one mile is driven, $\$0.75\times2$ if two miles are driven, etc. This shows us that the cost increases by $\$0.75$ for each mile driven. Therefore, the correct formula will include a term that multiplies $\$0.75$ by the number of miles driven.