PLEASE HELP ME!

For 60 students in a large class, 12 marks are added to each score to boost the students' scores on a relatively difficult test.

a) Knowing that sigma (x+12)=4404, find the mean score of this group of 60 students.

b) Another section of the class has 40 students and their average score is 67.4. Find the average of the whole class of 100 students.

Afarmer has a large field that is x feet in length. he wants to fence in a rectangular section in the middle of the field , leaving a length of 100 feet of open field behind each end of the fenced rectangle.he also wants the width of the fenced-in space to be 100 feet less than its length. find the expressions to represent the length and width of the fenced section of the field