explain how to get to the answers asap

Question 1
 Part A:
 We must evaluate the following intervals:
 if d> = 5:
 The function for this case is:
 C = 4.70d
 if d <5:
 The function for this case is:
 C = 4.70d - 1
 Part B: 
 We evaluate the functions corresponding to the number of days:
 For d = 4
 C = 4.70 * (4) - 1 = 17.8 $
 For d = 7
 C = 4.70 * (7) = 32.9 $
 
 option 3
 Question 2:
 For this case, what you should do is find the linear function that best suits the problem.
 We have then:
 y = 3x + 3
 We evaluate for different values of x to compare with the table:
 f (0) = 3 (0) + 3 = 3
 f (1) = 3 (1) + 3 = 6
 f (2) = 3 (2) + 3 = 9
 f (3) = 3 (3) + 3 = 12
 f (4) = 3 (4) + 3 = 15
 We observe that all the values coincide with the table.
 
 option 2.