For this lab, you will write a program that analyzes grades. The file grades $.$ txt $($located below this lab in D$2$L$)$ contains a list of student grades from an arbitrary number of sections.

Each line contains the student ID number, the section number, and the final letter grade received, separated by a single tab. Your program should open this file and calculate the average score for each distinct section, keeping in mind that each file contains an unspecified number of sections.

Note: You may assume this file will always be in the same folder as your python file.

You can convert each letter grade to a number using the following table:

$A=100$

$B=89$

$C=79$

$D=74$

$F==69$

Remember, each section needs to have its own separate average.

Example Output:

Section $1$ average: $81\mathrm{.}943$

Section $2$ average: $81\mathrm{.}803$

Section $3$ average: $82\mathrm{.}108$

Section $4$ average: $82\mathrm{.}093$

Section $5$ average: $82\mathrm{.}61$